The Mayo Lung Project has been established to assess the effectiveness of close surveillance in reducing the death rate from bronchogenic carcinoma. Candidates for study are high-risk patients (men, aged 45 or older, smoking at least one pack of cigarettes daily) with life expectancy of at least 5 years. A lung-health questionnaire, chest roentgenogram, and 3-day pooled specimen of sputum provide the basic information. Candidates with positive test results receive appropriate treatment. Those whose initial data are negative are randomized into either a close-surveillance (participant) group or a control group. Participants are restudied every 4 months. Controls receive whatever medical care they ordinarily would, but no regular restudy except annual follow-up by letter. This routine will extend over 5 years or more, and tracing 5 to 10 years further. Lung-cancer death rates in the two groups will be compared. Preliminarily, it appears such programs can be incorporated into private group practices.