Acrolein and two of its more stable derivatives, the oxime and the diethylacetal, and the related allyl alcohol were given in drinking water to groups of 20 male and 20 female F344 rats at doses close to the maximum that could be tolerated by the animals, for most of their lifetime. Acetaldoxime served as a control for the hydroxylamine derivative of acrolein. Most of the tumors were common in untreated rats of this strain. Only adenomas of the adrenal cortex in females were more numerous than in untreated controls. Acrolein itself was too toxic to hamsters to conduct a carcinogenesis study. Acrolein oxime, acrolein diethylacetal and allyl alcohol were all quite toxic to hamsters, but 2 mg per week by gavage was tolerated by groups of 20 male Syrian hamsters. There was a small number of tumors of the pancreatic ducts and of the forestomach in the treated hamsters, but the incidence was not statistically significant.