The relation between tobacco use and leukemia was evaluated in a population-based case-control study of 578 white men with leukemia and 820 controls conducted in Iowa and Minnesota during 1981-1984. Risks were significantly elevated for all leukemia (odds ratio (OR) = 1.4) and chronic lymphocytic leukemia (OR = 1.6) for both tobacco users and cigarette smokers. There were significantly elevated risks for cigarette smokers of longest duration for all leukemia (OR = 1.6), chronic myelogenous leukemia (OR = 3.3), and chronic lymphocytic leukemia (OR = 1.6). Thus, the findings of this study provide additional support for an association between smoking and the risk of several types of leukemia.