The toxic hazards of exposure to 2-acetylaminofluorene (53963) (2- AAF) are discussed. Dietary dose response studies in rats are described in which induction times were determined for tumor development, especially liver and kidney tumors. Other studies are summarized on the incidence of eye, mammary, ear duct, and liver tumors in rats fed 2-AAF, and on the effects of other dietary components on 2-AAF carcinogenicity including casein (9000719), tryptophane (73223), indole (120729), vitamin-B6 (8059243), and liver powder. Cellular and biochemical changes caused by 2-AAF are described, such as development of nodular and non nodular foci in the liver; increases in glycogen, glucuronyl-transferase, glutathione-reductase, and uridinediphosphoglucose; and decreases in liver catalase, alkaline RNase, and serum alkaline RNase. The effect of hormones on 2-AAF carcinogenicity is discussed, and research findings are reviewed on 2-AAF carcinogenic antagonists, metabolic fate, and species differences in carcinogenic response. The author concludes that 2-AAF has been proven to be carcinogenic in rats, mice, rabbits, dogs, hamsters, and fowl, and should probably be considered as a human carcinogen.