Recently the Supreme Court of Pennsylvania overturned the Court of Appeals and rejected the notion that “each and every fiber” of asbestos amounted to a substantial cause of a given plaintiff’s disease and affirmed a trial court’s ruling excluding such testimony. The Court concluded that an expert’s testimony that “each and every” fiber of asbestos was a substantial cause of disease was in irreconcilable conflict with itself: “one cannot simultaneously maintain that single fiber among millions is substantially causative, while also conceding that a disease is dose responsive.” Id. at p. 48. In making this finding, the Court observed that while the expert in question had himself testified that three factors (potency, concentration, and duration) needed to be considered in estimating the relative effects of different exposures, the expert did not consider those three factors in arriving at his opinions. Id. at 48-49. This decision sets a strong precedent not only for Pennsylvania, but for the country, regarding the every-fiber theory.  It has been long argued by defendants that the every-fiber theory is in direct conflict with the concept of either dose/response, or any meaningful definition of “substantial cause”.  Thus, this ruling constitutes a significant victory for defendants in asbestos litigation and is certain to have nationwide impact and may indeed work to significantly curb the scientifically dubious assertion of single-fiber as a substantial contributing factor to asbestos related disease.