The increasing incidence of primary lung cancer has made it important to delineate the natural history of this grave disease so that improved detection techniques may be developed and populations at greatest risk may be pinpointed for intensive study. With this goal in mind, the Philadelphia Pulmonary Neoplasm Research Project was begun in December 1951. A total of 6,137 men 45 years of age or older volunteered to report semiannually over a ten-year period for x-ray examination of the chest and questioning about symptoms, smoking habits, etc.1 The men were recruited over a fouryear period and the study has now drawn to a close.
At the start of the project, in considering the symptoms which might be associated with lung cancer, the first one which came to mind was cough, long recognized as a symptom of lower-respiratorytract disease. The prevalence of cough increases with increasing age and increasing degrees