In 1953 we began in Japan a lung cancer detection program by chest X-ray surveys amongst several groups including employees of the Tokyo Metropolitan Government (TMG). The results obtained from this 27-year survey indicate that chest X-rays are effective in the detection of early stage lung cancer located peripherally but not centrally in the lung. At the Department of Surgery, Tokyo Medical College, 54 cases of early stage lung cancer were treated; 45 cases were peripheral and only nine cases were central. Of the nine centrally located tumors only two (22%) were detected by chest X-ray survey, as opposed to 71% of the peripheral-type cases similarly detected. Sputum cytology surveys have thus gained increasing attention in Japan for the detection of early stage central lung cancer, particularly in cases where the chest X-ray is negative. A sputum cytology study is thus being conducted amongst high risk employees of the TMG as well as amongst local residents of the Itabashi area in Tokyo aged 40 years and over, but the results are as yet inconclusive. However, in addition to detecting early stage lung cancer, the objective of sputum cytology surveys should include the detection of atypical squamous cell metaplasia, since this condition has been shown experimentally [Kato et al., this Symposium] and clinically [1, 17, 18, 21] to be involved in the development of squamous cell carcinoma. Squamous cell metaplasia is therefore checked for in our survey cases, and chronological changes of nuclear atypia are monitored. Our chest X-ray survey of employees of the TMG is a representative study that has been carried out over a long period of time. There are several other groups conducting sputum cytology and/or chest X-ray surveys in Japan, particularly the National Kinki Central Hospital Group, where two of us (K.S. and K.F.) have initiated a chest X-ray and sputum cytology project which has yielded a high rate of lung cancer detection.