OPINION OF THE COURT
SLOVITER, Circuit Judge.
Dismissal of an action on the grounds of the statute of limitations is particularly anguishing when the victim is a minor, the injury grievous, and the alleged wrongful act repellent, if true. See O’Brien v. Eli Lilly & Co., 668 F.2d 704, 712 (3d Cir.1982) (Sloviter, J., concurring). Nonetheless, we are obliged to follow the applicable legal principles. Certainly a federal court sitting in diversity is not free to impose its notions of equity on state courts or on a state legislative body. We will affirm the entry of judgment for defendant in this case because we believe that Pennsylvania law requires us to do so.
I.
Julie Beth Urland and her parents William and Chloe Urland filed suit against Merrell-Dow Pharmaceuticals, Inc., the manufacturer of Bendectin, contending that Mrs. Urland’s ingestion of Bendectin while pregnant was the cause of Julie’s birth defects. Julie was born on February 8, 1972, with part of her left arm missing. This diversity action was filed on October 7, 1981 against Merrell-Dow in the United States District Court for the Eastern District of Pennsylvania. Merrell-Dow pled the two year Pennsylvania statute of limitations as a defense. The court bifurcated the statute of limitations issue, presenting that issue to the jury as a threshold matter.
II.
Following Julie’s birth, the Urlands suspected that Mrs. Urland’s ingestion of Bendectin might have been the cause of Julie’s birth defects and Mrs. Urland made various inquiries. In 1972, Mrs. Urland contacted several of her treating physicians, the March of Dimes, and the Food and Drug Administration. In her letter to the FDA, she stated that she had taken Bendectin “at the approximate time when the limb buds [were] being formed” and referred to “the questions and doubts” she had concerning this medication. App. at 391. Copies of this letter were sent to the Hon. Hugh Scott of Pennsylvania and Merrell-Dow, then Merrell-National Laboratories Division of Richardson-Merrell, Inc.
The FDA responded that it would refer the letter to the physicians who monitor adverse drug experience, and requested that Mrs. Urland’s physician complete the Drug Experience Report which it enclosed. Apparently, this was not done. Senator Scott wrote that he was referring the letter to the appropriate authorities.
Merrell-Dow also responded by letter from Richard H. O’Dillon, M.D., Director of the Product Development Clinical Research Group who stated that the letter was written for the purpose of “relievpng] your mind about your use of Bendectin during pregnancy.” App. at 394. Dr. O’Dillon described various animal and human tests purportedly showing that Bendectin was not an agent having the potential for causing malformations and stated his “belief, that your child’s malformation is unrelated to Bendectin ingestion.” App. at 394. The Urlands claim that as a result, they did not sue Merrell-Dow at that time. Nevertheless, the Urlands continued to harbor suspicion that Bendectin was the cause of Julie’s birth defects and discussed the possibility of bringing a lawsuit against Merrell-Dow.
In early September 1979, the Urlands were contacted by telephone by a reporter from the National Enquirer who stated that Mrs. Urland’s letters had come to light in a trial in Florida involving Bendectin and birth defects. After the phone call Mrs. Urland told her husband about the Florida suit and the allegation made there that Bendectin caused birth defects. Mrs. Ur-land agreed to meet with the reporter and at that meeting told him that she was suspicious that Bendectin caused Julie’s birth defects. Mrs. Urland also agreed to allow a picture of herself and Julie to be used in [1271]*1271an article concerning Bendectin to be published by the Enquirer. The front page headline on the National Enquirer dated October 9, 1979 stated “New Thalidomide-Type Scandel — Experts Reveal ... COMMON DRUG CAUSING DEFORMED BABIES.” App. at 397. The article quoted various medical sources as stating that Bendectin could cause birth defects, and described various cases of babies born with birth defects from mothers who had taken Bendectin during their pregnancy. The article also described an alleged coverup by Merrell-Dow of the test results indicating possible teratogenicity. The Urlands testified that they were not certain exactly when they purchased a copy of the National Enquirer edition containing their story, although Mr. Urland testified that he thought that he had purchased a copy on October 9, 1979, less than two years before the filing of the present lawsuit. However, he admitted he might have used that date because it appears on the newspaper. Mrs. Urland testified that she had since become aware that the edition dated October 9, 1979 hit the newsstands on October 2,1979, and went off the newsstands on October 9, 1979.
It is clear that the interview with the reporter took place in September 1979, that at the time of the reporter’s phone call Mrs. Urland became aware of the Florida trial alleging a connection between Bendectin and birth defects, and that this information revived her suspicion about Bendectin being a possible cause of Julie’s birth defects.
III.
The applicable statute of limitations is set forth in 42 Pa.Cons.Stat.Ann. § 5524(2), which states that an action to recover damages for personal injuries must be commenced within two years. However, the Pennsylvania Supreme Court recognizes an exception to the statute, asserted by the Urlands before the district court, which delays the running of the statute until the plaintiff knew, or through the exercise of reasonable diligence should have known, of the injury and its cause. Ayers v. Morgan, 397 Pa. 282, 292, 154 A.2d 788, 793 (1959). See also Pocono International Raceway, Inc. v. Pocono Produce, Inc., 503 Pa. 80, 85, 468 A.2d 468, 471 (1983).
In a recent explication of the discovery rulé, the Pennsylvania Superior Court has set forth the applicable standard as whether “the plaintiff knows, or reasonably should know: (1) that he has been injured, and (2) that his injury has been caused by another party’s conduct.” Cathcart v. Keene Industrial Insulation, 324 Pa.Super. 123, 136-37, 471 A.2d 493, 500 (1984) (in banc) (footnote omitted). The Cathcart standard has been widely adopted by Pennsylvania courts, see, e.g., Wheeler v. Johns-Manville Corp., 342 Pa.Super. 473, 476-77, 493 A.2d 120, 122 (1985), and has likewise been applied in decisions of this court. See, e.g., Cowgill v. Raymark Industries, Inc., 780 F.2d 324, 330 (3d Cir.1986).
The Urlands relied in addition upon the equitable rule that a defendant will be es-topped from asserting the statute of limitations if through fraud or concealment the defendant causes the plaintiff to relax vigilance or deviate from the right of inquiry. Nesbitt v. Erie Coach Co., 416 Pa. 89, 92, 204 A.2d 473, 475 (1964). See also Ciccarelli v. Carey Canadian Mines Ltd., 757 F.2d 548, 556 (3d Cir.1985). A party relying on this doctrine will be entitled to a tolling of the statute of limitations by proving that there has been either intentional or unintentional deception by the defendant. Nesbitt, 416 Pa. at 96, 204 A.2d at 475-76. See also Ciccarelli, 757 F.2d at 556. The district court accepted arguendo the Ur-lands’ position that Merrell-Dow concealed the potential claim, and it instructed the jury, over Merrell-Dow’s objection, to assume for purposes of the statute of limitations phase of the case that the 1972 letter written by Dr. O’Dillon to the Urlands was inaccurate and misleading.1 By assuming [1272]*1272the existence of fraudulent concealment, the district court concluded that the issue of whether the Urlands were time-barred hinged solely on whether they knew or should have known prior to October 7,1979 that Bendectin was the operative cause of Julie’s birth defect.
The jury was given the following interrogatory:
Have Mr. and Mrs. Urland proved by a preponderance of the evidence that neither of them knew, or exercising reasonable diligence should have known, before October 7, 1979, that Bendectin was an operative cause of Julie Beth Urland’s birth defect as alleged in their complaint?
(_) (_)
YES NO
(A “Yes” answer is in favor of Mr. and Mrs. Urland. A “No” answer is in favor of Merrell Dow Pharmaceuticals, Inc., and will terminate the case.)
The jury responded “no” to the interrogatory, and the district court entered judgment in favor of Merrell-Dow. The Ur-lands appeal, challenging various rulings of the district court.
IV.
Fraudulent Concealment
A.
The Urlands’ principal argument on appeal is that the district court failed to appreciate the differences in the effect on the statute of limitations between the discovery rule and fraudulent concealment. They concede that under the discovery rule, the statute of limitations begins to run when plaintiffs knew or using reasonable diligence should have known of the claim. They contend, however, that under the fraudulent concealment doctrine, which they also term “the doctrine of estoppel,” the “defendant is ‘stopped’ from raising the defense of the statute of limitations until such time as the plaintiff has actual knowledge of the fraudulent activity and the true nature of the events.” Reply Brief at 4 (emphasis in original). Although it is questionable whether the Urlands preserved this argument in the district court,2 we reach the merits of the argument because it may touch upon plaintiffs’ objection that they were entitled to a separate instruction regarding the effect of fraudulent concealment on Merrell-Dow’s statute of limitations defense.
We reject at the outset the Urlands’ extreme contention, which was reflected in the only written request for jury instruction on this issue that they submitted to the court, that Merrell-Dow was not entitled to use the statute of limitations defense at all. Plaintiffs cite as authority the language of this court’s opinion in Ciccarelli v. Carey Canadian Mines, Ltd., 757 F.2d 548, 556 (3d Cir.1985), where, in an expansive discourse on the statute of limitations, we stated, “if through fraud or concealment the defendant causes the plaintiff to relax [1273]*1273vigilance or deviate from the right of inquiry, the defendant is estopped from invoking the bar of limitation of action.” Because we were concentrating in Ciccarelli on what constitutes fraudulent concealment and we concluded that there was no fraudulent concealment in that case, we may not have honed the dictum on which plaintiffs rely as carefully as we should have. It is evident from the Pennsylvania cases cited in Ciccctrelli that we did not suggest, as plaintiffs argue, that the defendant would never be able to use the statute of limitations as a defense if there had been fraudulent concealment. Those cases either failed to address the question of whether a defendant, once estopped, would ever later be able to invoke the statute of limitations, see Gravinese v. Johns-Manville Corp., 324 Pa.Super. 432, 441-42, 471 A.2d 1233, 1238 (1984); McNair v. Weikers, 300 Pa.Super. 379, 388-89, 446 A.2d 905, 909 (1982), or resolved the issue adversely to the Urlands. See Nesbitt, 416 Pa. at 96, 204 A.2d at 477; Schaffer v. Larzelere, 410 Pa. 402, 405-06, 189 A.2d 267, 270 (1963). Thus, we agree with the district court that “the mere fact that there’s fraud does not mean that the statute is always gone. It only means that it’s tolled until the effects of the fraud have been nullified by knowledge to the plaintiff.” App. at 187.
We turn instead to the question of when, under Pennsylvania law, the statute of limitations begins to run when fraudulent concealment has been shown or, as in this case, assumed to have been shown. No Pennsylvania case suggests that the reasonable diligence standard applied to the tolling of the statute of limitations for purposes of the discovery rule is not also applicable when the plaintiff relies on fraudulent concealment for tolling. Although there is language in Pennsylvania cases that speaks of the statute being tolled “until actual knowledge arises,” see Schwab v. Cornell, 306 Pa. 536, 540,160 A. 449, 450 (1932), those cases were decided without reference to the distinction now under consideration. For example, in Schwab the plaintiff brought suit against a conveyancer who failed to inform him of the evidence of certain unpaid taxes and instead advised him that the title was entirely clear of liens with one exception. The Court held the statute was tolled until plaintiff discovered the actual situation by receiving notice that his property had been sold for the unpaid taxes. Under these circumstances, there was no need to discuss reasonable diligence. Again, the “actual knowledge” language taken from Schwab was used in Nesbitt v. Erie Coach Co., 416 Pa. at 96, 204 A.2d at 477 (1964), but that was another case where there appears to have been no basis in the facts to discuss the reasonable diligence standard.
It is evident from the Pennsylvania cases, however, that the Supreme Court of that state views tolling of the statute of limitations in terms of the same “knew or should have known” standard whether the statute is tolled because of the discovery rule or because of fraudulent concealment. For example, in the leading case of Smith v. Blachley, 198 Pa. 173, 47 A. 985 (1901), the Court stated, “in general ... in cases of fraud the statute runs only from discovery, or from when, with reasonable diligence, there ought to have been discovery.” Id. at 175, 47 A. at 985.
The general rule was reiterated in Deemer v. Weaver, 324 Pa. 85, 187 A. 215 (1936), where the Court, in finding that the defendant had concealed her fraud upon the plaintiffs and that the plaintiffs were not otherwise put on notice, stated:
If by any act of concealment or deceit, whether before or at the same time or after the act is committed, the wrongdoer hides from the innocent party the facts which would put him upon inquiry, the statute does not begin to run.
Id. at 88, 187 A. at 216. The Court further stated:
There are very few facts which diligence cannot discover, but there must be some reason to awaken inquiry and direct diligence in the channel in which it would be successful. This is what is meant by reasonable diligence.
[1274]*1274Id., at 90, 187 A. at 217 (quoting Maul v. Rider, 59 Pa. 167, 171 (1868)). Similar “reasonable diligence” language was used in Schaffer v. Larzelere, 410 Pa. 402, 406,189 A.2d 267, 270 (1963) (“if it is true ... that the defendants deliberately concealed the facts incident to the cause of decedent's death and that the plaintiff could not through the use of reasonable diligence have ascertained these facts, this would bar the defendants from invoking the defense of the statute.”) See also Ebbert v. Plymouth Oil Co., 348 Pa. 129, 137, 34 A.2d 493, 497 (1943); Barr v. Luckenbill, 351 Pa. 508, 513, 41 A.2d 627, 629 (1945).
In any event, this court already has had occasion to consider the applicable rule under Pennsylvania law in a civil rights case where the plaintiff claimed that the defendant county and various of its officials were estopped from asserting the statute of limitations because of their actions in concealing the circumstances of the plaintiffs decedent’s death while in police custody. See Swietlowich v. County of Bucks, 610 F.2d 1157 (3d Cir.1979). We stated: “Pennsylvania courts hold that the limitation period does not commence in cases of fraudulent concealment until the time of discovery or the date when with reasonable diligence one would have been led to discovery.” Id. at 1162 (emphasis added). This was consistent with our prior reading set forth in Williams v. Pittsburgh Terminal Coal Corp., 62 F.2d 924 (3d Cir.), cert. denied, 289 U.S. 749, 53 S.Ct. 692, 77 L.Ed. 1494 (1933), where we stated the Pennsylvania rule as follows:
But the statute does not begin to run where the facts are suppressed and deliberately concealed from the plaintiff. Such conduct tolls the statute, and in that case it does not begin to run until the plaintiff has knowledge of the facts constituting the cause of action or by reasonable diligence should have had such knowledge.
Id. at 925 (emphasis added).
The Pennsylvania cases following Swietlowich reinforce our interpretation of Pennsylvania law set forth in that case. In Rothman v. Fillette, 503 Pa. 259, 266 n. 3, 469 A.2d 543, 546 n. 3 (1983), the Court stated: “the law is clear that fraud or deceit tolls the statute of limitations until such time as the fraud has been discovered by the exercise of due diligence.” Even more pertinent is the recent opinion of the Pennsylvania Commonwealth Court in Dudley v. Workmen’s Compensation Appeal Board, 80 Pa.Cmwlth. 233, 471 A.2d 169 (1984). There, the court stated that, “[t]he ‘discovery rule,’ applicable to medical malpractice actions, is a closely related application of estoppel principles where fraud or deception, intentional or otherwise, may cause a potential plaintiff to fail to file a claim within the statutory period.” Id. at 239, 471 A.2d at 172. After stating that under the discovery rule, “ ‘the statute of limitations does not begin to run until such time as the injury’s existence is known or discovered, or becomes knowable or discoverable by the exercise of reasonable diligence,’ ” id. at 240, 471 A.2d at 172 (citation omitted), the court proceeded to apply the same standard to the fraudulent concealment cases: “When an employer, through its acts or statements, lulls a claimant into a false sense of security regarding the filing of a workmen’s compensation claim, those actions, whether intentional or unintentional, toll the running of the limitations period of section 315 of the Act. That period reasonably should not begin until the claimant knows, or with reasonable diligence could know, of his deception.” Id. at 241, 471 A.2d at 173 (footnote omitted).
We therefore reject the Urlands' contention that Pennsylvania would not apply the reasonable diligence test in fraudulent concealment cases.
B.
The Urlands also argue that the district court improperly refused to allow them to introduce evidence purporting to show fraudulent concealment by Merrell-Dow of test results showing that Bendectin causes birth defects. The district court refused to admit such testimony because it assumed concealment for purposes of the inquiry on the statute of limitations and [1275]*1275therefore instructed the jury that they should assume that the O’Dillon letter was false and misleading. Thus, the court explained:
The only thing, as far as her state of mind is concerned, the only thing that is relevant is the information that she received from her inquiries. One of which is the O’Dillon response.
App. at 207. The Urlands argue that evidence of the purported fraud was necessary to show the “nature, quality and extent of the fraud and how it touched the Urlands not only through the O’Dillon letter but through their other contacts with the medical community.” Appellant’s Brief at 19.3 •
However, because the district court had instructed the jury to assume that the O’Dillon letter was false and misleading, it did not abuse its discretion in rejecting any further evidence on the concealment issue. It could have reasonably decided not to embark on the complex issue of whether, in fact, Merrell-Dow had concealed relevant and damaging test results in the context of the threshold decision of the statute of limitations. See Fed.R.Evid. 403.
V.
Discovery
The Urlands argue that the district court erred in charging the jury that they must determine whether the Urlands knew or should have known “that Bendectin was an operative cause of the birth defect.” App. at 356. The Urlands argue that knowledge that Bendectin caused their daughter’s birth defect is not itself sufficient to start the statute running, but rather that they were required to know of a causal connection between the birth defect and Merrell-Dow’s conduct.
In Pennsylvania, the relevant inquiry for purposes of the statute of limitations is whether plaintiffs knew or reasonably should have known of the causal relationship between the injury and conduct causing that injury. Cathcart v. Keene Industrial Insulation, 324 Pa.Super. at 136-37, 471 A.2d at 500. However, plaintiffs need not know that they have a cause of action or that the injury was caused by another party’s wrongful conduct. See Chandler v. Johns-Manville Corp., 352 Pa. Super. 326, 330-31, 507 A.2d 1253, 1255-56 (1986); Price v. Johns-Manville Corp., 336 Pa.Super. 133, 137-39, 485 A.2d 466, 468-69 (1984); DeMartino v. Albert Einstein Medical Center, Northern Division, 313 Pa.Super. 492, 499-503, 460 A.2d 295, 298-300 (1983). “[Ojnce [a plaintiff] possesses the salient facts concerning the occurrence of his injury and who or what caused it, he has the ability to investigate and pursue his claim.” Berardi v. Johns-Manville Corp., 334 Pa.Super. 36, 44, 482 A.2d 1067, 1071 (1984) (emphasis in original) (quoting Staiano v. Johns Manville Corp., 304 Pa.Super. 280, 288, 450 A.2d 681, 685 (1982)). In this case plaintiffs were clearly aware of Merrell-Dow’s identity and its connection with the drug, and thus the court’s charge was not error.
The Urlands object to an example given to the jury by the district court to illustrate the notion of operative cause. In a supplemental instruction, the court stated:
Let me give you another example. Suppose at lunch you ate a lot of watermelon and fruit and your stomach is not feeling so good. You might say the fruit caused my upset stomach. That’s the kind of thing we’re talking about now. None of you are physicians, so you can’t really give a medical opinion on causation, but you have, you know your body and you know what upsets your stomach and you can tell. That’s the type of causation we are talking about.
App. at 379. The court explained to the jury that the causation to be considered in applying the discovery test is “[n]othing technical, nothing legal, nothing medical, [1276]*1276but ordinary causation that we speak about every day. Cause and effect that we speak about every day.” App. at 379.
The Urlands argue that the watermelon example does not focus upon the relationship between the injury and Merrell-Dow’s conduct. However, the Urlands did not object to the instruction on this ground before the district court. In any event, looking at the instructions as a whole, we find no error.
VI.
Minor’s Tolling Statute
Finally, the Urlands argue that even if they are barred by operation of the Pennsylvania discovery rule, the claim of their daughter Julie was revived by 42 Pa.Cons. Stat.Ann. § 5533(b), which provides that the statute of limitations cannot run against a child during the period of minority.4 We reject Merrell-Dow’s contention that the Urlands did not preserve this contention, and therefore turn to its merits.
Under prior Pennsylvania law, minors were subject to the adult statute of limitations. See, e.g., Walters v. Ditzler, 424 Pa. 445, 450, 227 A.2d 833, 835 (1967). The minor’s tolling statute was enacted on May 30, 1984, effective 30 days thereafter. Under Pennsylvania law, “after an action has become barred by an existing statute of limitations, no subsequent legislation will remove the bar or revive the action.” Overmiller v. D.E. Horn & Co., 191 Pa.Super. 562, 568, 159 A.2d 245, 248 (1960); see Clark v. Jeter, 358 Pa.Super. 550, 555, 518 A.2d 276, 278 (1986); Petition of Weigand, 214 Pa.Super. 371, 374-75, 257 A.2d 627, 629 (1969).
Thus, it has consistently been held that the minor’s tolling statute does not act to revive claims that had already been barred by the applicable statute of limitations pri- or to the effective date of the Act. See Redenz v. Rosenberg, 360 Pa.Super. 430, 434-35, 520 A.2d 883, 885 (1987); Lewis v. City of Philadelphia, 360 Pa.Super. 412, 416, 520 A.2d 874, 876 (1987); Maycock v. Gravely Corp., 352 Pa.Super. 421, 425-28, 508 A.2d 330, 333-34 (1986); see also Robinson v. Kelly, No. 86-4484, slip op. at 2 (E.D.Pa. Mar. 31, 1987) [Available on WESTLAW, DCT database]; Orozco v. Children’s Hospital of Philadelphia, 638 F.Supp. 280, 283-84 (E.D.Pa.1986). Because the jury found that the Urlands’ claim had been barred by the time they brought their action on October 7,1981, Julie’s claim could not be revived by the subsequent enactment of the minor’s tolling statute.
The Urlands argue, relying on 1 Pa.Cons. Stat.Ann. § 1928(c),5 that we should construe the minor’s tolling statute liberally to effectuate its remedial and humanitarian purposes. However, the Pennsylvania courts found nothing in the legislative history of the minor's tolling statute indicating that the General Assembly intended the Act to apply to previously barred claims, and we are bound to follow their interpretation of their own statutes.6
VII.
Conclusion
We find no reversible error. We stress that in this case, the district court did not decide in favor of Merrell-Dow’s statute of limitations defense on a pre-trial motion. Instead, the issue was fairly presented to a jury, which decided the relevant factual question adversely to the Urlands. The [1277]*1277Urlands do not argue on appeal that there was insufficient evidence to support the jury’s verdict.
For the reasons stated, the order of the district court entering judgment in favor of Merrell-Dow will be affirmed.