The chest X-ray and sputum cytology are the only screening tests currently available for detecting presymptomatic lung cancer and they complement each other. There are several examples in the literature of cytologic diagnosis of lung cancer in the absence of radiographic findings. These are usually central lesions. In some cases in situ lesions were recognized cytologically. Radiographic detection of lung cancer in an asymptomatic stage is most effective in peripheral lesions where the cytologic method has a lower yield. Multiple-day sputum cytology examinations have greater diagnostic accuracy than single-day tests. The high-risk group of candidates for screening for lung cancer consists of middle-aged and older men who are chronic, excessive cigarette smokers. Recently, there has been an alarming rise in the incidence of lung cancer among women of similar age and smoking habits, but this has not yet become great enough to consider them as screening candidates. Early data suggest that radiologic and cytologic screening for lung cancer every 4 mo. may benefit the high-risk group of middle-aged and older men who are chronic heavy smokers. There is no strong statistical support for screening any other population, but if present smoking and lung cancer trends among women continue, there soon may be.