Lifetime tests were done in NZR inbred rats of dimethylnitramine (DMNO) by addition to the drinking water (average dose 1.83 g/kg body weight) and in NZO mice by repeated subcutaneous injection from birth to 7 months of age followed by administration in drinking water (total average dose 4.72 g/kg body weight). Rats developed hepatocellular carcinomas (85%), some of which metastasized. Mice developed hepatocellular carcinomas (81%) and renal adenocarcinomas (48%). Statistically significant increases of other tumor types also occurred in mice. The main targets for DMNO carcinogenesis appeared to be the liver cell epithelium and, at higher dose rates, renal tubular epithelium.