Scientific opportunities generally arise when two or more research areas converge and/or advances in methodology occur. This occurred at the turn of the 19th century in the field of infectious bacterial and fungal diseases. As we draw near to the 21st century, research in the laboratory is providing us with both critical information on mechanisms of carcinogenesis and new technological advancements, including those in immunology, biochemistry, and molecular biology. Investigations in the field of epidemiology have clearly demonstrated the importance of environmental exposure to carcinogens and have identified populations at high cancer risk. It is now practical to integrate laboratory determinations into classic epidemiological approaches. Several markers, e.g., carcinogen-DNA adducts, related to tumor initiation and perhaps to tumor conversion, are currently being evaluated. We also need to develop indicators of tumor promotion and progression. The potential of biochemical and molecular epidemiology to predict cancer risk in an individual prior to the onset of clinically evident cancer provides an exciting new opportunity in cancer research and prevention.