The paper describes a method for adjusting the analysis of occupational/environmental lung cancer risks for the effects of cigarette smoking in cohort and case-control studies. The method uses a function that relates an individual's death rate to his age and cigarette smoking history. Two such functions are examined. The first depends on total packs of cigarettes smoked and age. The second, based on the multistage theory of carcinogenesis, depends on age, age at start of smoking, and subsequent smoking rates. The lung cancer rates predicted by these two functions are compared to those observed in cohort studies of male British physicians and U.S. veterans, and in a case-control study of non-Hispanic white men in New Mexico. Neither of the cohort data sets distinguished the fit of the two functions. The New Mexico data were fit better by the second function, though both functions overpredicted death rates among ex-smokers. Each function explained substantially more variation in the New Mexico data than did any of several logistic regression models involving categorical variables for age and smoking. (Copyright (c) 1988 by John Wiley & Sons, Ltd.)