Mortality or incidence rates of ten major neoplasms in migrants from several countries, their respective countries of origin, their American-born offspring, and United States whites were compared. Rates in succeeding generations of Americans increased most rapidly for colon cancer and most slowly for breast cancer, with ovarian cancer occupying an intermediate position and prostate cancer showing inconsistent patterns of displacement of rates among various ethnic groups. Rates of stomach, liver, and esophageal cancers declined rapidly in succeeding generations of migrants, although small residual excess risks compared to whites persisted in second generation Americans. These residual excesses were greatest for stomach cancer and least for cancer of the esophagus. Differences in rates of lung and bladder cancers were commensurate with differences in smoking patterns among the generations and ethnic groups considered. This was also true for pancreatic cancer in Asians, but not in Latin Americans. The etiological implications of these observations are discussed.