The toxic hazards of exposure to N-nitrosodimethylamine (62759) (DMN) are discussed. The first extensive investigation of DMN toxicity is described in response to two reported cases of cirrhosis of the liver in exposed workers. The results from these studies are reviewed, including acute lethal doses in rats, rabbits, mice, guinea-pigs, and dogs, and chronic effects in rats. Findings are also summarized from numerous other acute and chronic toxicity tests, such as induction of liver damage and hepatic tumors in rats, rabbits, mice, and guinea-pigs. Dose relationships are discussed along with effects other than liver tumors, including kidney tumors, lung tumors, and ethmoid carcinoma. The carcinogenicity of N- nitrosodiethylamine (55185) in monkeys is described in lieu of available data on DMN carcinogenicity in nonhuman primates. Tumor induction times, total incidence, survival times, and histologic type of tumor are described. The author concludes that DMN has been shown to be carcinogenic in a variety of animal species by several routes of administration. DMN should be considered as a potential carcinogen for humans.