Screening for lung cancer by chest roentgenography and sputum cytology can be conducted by mail. Detection, localization, and treatment of early presymptomatic lesions are possible. The initial prevalence of lung cancer in men older than age 45 years who were heavy smokers was almost 1%. Rescreening at 4-monthly intervals detected 4.7 new cases of lung cancer per 1,000 subjects per year. Three times as many postsurgical stage I lesions were detected in the screened group as in the control group. Although survival seems to have been improved by screening, mortality from lung cancer is not yet significantly different in the 4-monthly surveillance and control groups. Longer follow-up is necessary for determination of the ultimate usefulness of screening.