The carcinogenicity of Farfugium japonicum and Senecio cannabifolius was studied in ACI rats. In Group I, rats were given a diet containing 20% Farfugium japonicum. Groups II, III, IV and V were given diets containing 8%, 4%, 1% and 0.2% Senecio cannabifolius until the end of the experiment, respectively. The experiment was terminated after 480 days, except for Group V which was terminated 560 days after the start of feeding. Hemangioendothelial sarcoma of the liver and liver cell adenoma were induced in Groups I, IV and V. All rats in Groups II and III died of hepatotoxicity within a short period.