Chronic toxicity of 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), which had been widely used in Japan as a food additive, was studied in both sexes of ICR/JCL mice by feeding a diet containing AF-2 in a concentration of 0.4% or 0.08%. The experiments confirmed its definite carcinogenicity in the forestomach, with dose dependency; more than 70% of mice fed the higher dose developed tumors, the majority of which were squamous cell carcinomas with metastatic growths, whereas, with a lower dose, fewer tumors occurred, following a longer latent period. In addition, possible leukemogenicity was suggested by a higher incidence in AF-2-fed females (10.8%) over that in control females (3.2%). The development of non-neoplastic lesions in the liver and kidneys, and of amyloidosis in various organs was also observed in some of AF-2-fed mice.