An animal model of bowel cancer, induced by 1,2-dimethyl hydrazine, has been developed in the Nb rat. Invasive polypoid carcinomas of the colon were noted in nine rats surviving 29 weeks after the carcinogen was first administered. Two of these nine rats also developed duodenal carcinomas. Because dosage schedules are known from previous experiments with the Nb rat, this animal model may be useful for evaluating the effects of cytotoxic drugs on experimental bowel cancer.