AbstractTissue samples from lung cancer patients who had worked at a copper smelter and from controls were collected and classified by a panel of pathologists: 38% of the cancers were found to be adenocarcinomas, compared to 12% among the controls, a statistically significant difference (p<0.05). The predominance of adenocarcinomas was associated with arsenic exposure. This finding is not consistent with Kreyberg's hypothesis that small‐cell undifferentiated and epidermoid carcinomas are the only type that increase in response to inhaled carcinogens [1962