This paper describes the history of the epidemiologic research on lung cancer prior to 1970 and its effect on chronic disease epidemiology. In the 1 930s, epidemiology was largely concerned with acute infectious diseases. As the evidence grew that the incidence of lung cancer was increasing among men, however, epidemiologists undertook research into the etiology of the disease. In 1950, Doll and Hill, in England, and Wynder and Graham, in the United States, published substantial case-control studies that implicated the use of tobacco as a major risk factor for the disease. A controversy developed over the credibility of this finding and was increased in 1954 when a cohort study by Doll and Hill and another by Hammond and Horn each gave estimates that the risk of lung cancer was greatly increased among smokers relative to the risk among comparable non-smokers. An account is given of the disputes surrounding these and related studies. The controversy had a stimulating effect in fostering the developing discipline of chronic disease and epidemiology.Wade Hampton Frost, the first profession of epidemiology in the United States, described epidemiology in 1926 as concerned largely with the mass phenomena of infectious disease [1]. He did point out, however, that the limits of the discipline had become somewhat vague. It was customary to include in epidemiology the study of infections which were not characterized by distinctive epidemics, since these diseases had much in common with traditional epidemic diseases. He did not specifically include the effects of famine, which, on account of its role in dramatic depopulation, had often been linked with pestilence, but he did include a food deficiency disease, scurvy, and he also included goiter, which, like the others, could be profitably considered, in relation to the population at risk, a characteristic epidemiologic concept.In the nineteen thirties, epidemiology was still concerned almost entirely with acute infectious diseases. Chronic diseases were becoming more important in the health field as a whole, however, partly in a relative sense because of the control of many infections, but also, to some extent, because of an increase in the incidence rate of certain chronic diseases. J.N. Morris, writing about British mortality data on middle-aged men, noted that as early as the 1 920s death rates from coronary heart disease and lung cancer in men had been increasing. In a later part of his book he referred to these diseases as causing modern epidemics [2]. They showed a sustained, rather than an episodic, increase, less dramatic than a classic epidemic, but, like the latter, they invited attention by reason of the number of people affected.A few small-scale epidemiologic investigations of the etiology of chronic disease had already been undertaken by the thirties. The rising interest in the field is illustrated by 29