Nitrosodi-n-propylamine, nitrosodi-n-butylamine and the ketone nitrosobis(2-oxopropyl)amine were administered by gavage to F344 rats at doses of 1 and 2 mmol for 30 weeks. The higher level of nitrosodipropylamine led to death of all the animals with carcinomas of the liver, nasal cavity and esophagus by the 40th week. At the lower level the rats died of these tumors but survived to week 60. In contrast, 1 mmol of nitrosobis(2-oxopropyl)amine did not cause death of all the animals until week 95, and fewer than half of them had liver carcinomas; none had tumors of the esophagus or nasal cavity. Nitrosodi-n-butylamine was a much weaker carcinogen than nitrosodipropylamine, since 80% of the rats given 2 mmol survived until week 83. Although, with this compound, the lifespan of the rats was not greatly shortened, a large variety of tumors was induced; about 60% of the animals had liver carcinomas, 50% forestomach carcinomas and 35% transitional cell carcinomas of the urinary bladder.