Two thousand one hundred and twelve male cigarette smokers over the age of 40, who either suffered from chronic bronchitis, showed long standing radiologic abnormalities, or recently recovered from pneumonia—or who showed another factor making them particularly prone to development of cancer of the lung—were screened with sputum cytology and chest x‐ray. Incidence of lung cancer was high: 17 cases (1 in 125 persons screened) were discovered. Eight of these cases were detected by x‐ray alone, 7 by cytology alone, and only 2 by both of these methods. This suggests that these screening techniques are deficient when used alone. Further confirmation of this is derived from investigation of 228 patients who were screened with negative results in 1965—9 of them developed and then succumbed to lung cancer, and at least 5 of them presumably had it at the time of initial screening. In screening programs an effort should be made not to give the participants a false sense of security concerning absence of lung cancer when results of screening tests are negative. Of the 17 cases, 13 died from cancer of the lung and one from another cause. Three are alive and well. The poor survival in this group was due, to an appreciable extent, to the fact that the same selective factors, such as chronic bronchitis, which rendered these patients liable to lung cancer precluded the possibility of surgical treatment.