Joiner (P) worked as an electrician. This required P to work around transformers and the dielectric fluid used as a coolant got into his eyes, mouth and stuck to his arms and hands. In 1983, his employer discovered that the fluid in some of its transformers contained PCB's; which are hazardous to human health. In 1991, P was diagnosed with small cell lung cancer. He sued General Electric (D) because they manufactured transformer and dielectric fluid. P claimed that his cancer was a direct result of his exposure to the PCB's in D's transformers. D had also been a smoker for eight years, and there was a history of lung cancer in his family. D removed the case to federal court and then moved for summary judgment; there was no evidence P suffered significant exposure to PCB's, and there was no admissible scientific evidence that PCB's promoted P's cancer. The district court ruled that there was a genuine issue of material facts, but there was no evidence that P had been exposed and the testimony of his experts failed to show that there was a link between PCB exposure and small cell cancer. The case was dismissed. P appealed. The court of appeals reversed under a stringent standard of review based on the trial judge's exclusion of evidence. The Supreme Court granted certiorari.