An analysis of cigarette smoking habits and family and past histories of 494 lung cancer patients was undertaken to determine whether host factors in such patients could be related to cancer. In men, 35.8% of the patients with squamous cell carcinoma had family histories of cancer, which is significantly higher than the ratio in control subjects (P less than 0.05). In women, 58.3% of the patients with bronchoalveolar cell carcinoma had family histories of cancer, and, in six out of eight of them, their parents had had the disease. As for past histories, 7.7% of the women with lung cancer had undergone surgery ovarian tumor. These results suggest that familial (hereditary) factors and predisposition play a role in the etiology of lung cancer.