This paper describes the progressive changes in cancer incidence that have been observed among Japanese after their migration to Hawaii. It reviews descriptive and analytic epidemiologic data suggesting a role for genetic susceptibilities in explaining the high risk of Japanese for colon cancer and their low risk for lung cancer, when compared to Caucasians. Differences in certain pharmacogenetic polymorphisms may explain these risk patterns. This research may lead to a better characterization of cancer risk at the individual level and, consequently, to improved methods of prevention.