To study whether low-level exposure to asbestos contributes to lung cancer risk, the asbestos body (AB) content in lung tissue was measured in 476 patients with lung cancer and 369 patients with other diseases, all from a Japanese industrialized city. Eleven patients with histologically confirmed asbestosis were included. The findings were stratified into four groups. A significant number of patients with lung cancer were seen in the groups with high counts, as compared to controls. There was no significant difference in histologic type and site of lung cancer among four groups. The patients with lung cancer in high count groups were significantly younger than those with lower counts. A significant number of smokers were seen in the groups with high AB counts among patients with lung cancer as compared to controls, even if the patients with asbestosis were excluded. These findings suggest that there may be a positive interaction of smoking and exposure to asbestos relative to the incidence of lung cancer even at a low exposure level.