Experimentally induced gastric tumors in rats were first described by Fibiger in 1913 who attributed the tumor to nematodes in cockroaches eaten by the rats. Passey (1934) claimed the condition was due to Vit. A deficiency. Cramer (1937) concluded that parasite and diet were not sufficient to cause the tumors. Roffo (1938, 1939) thought that carcinogenic hydrocarbons were formed from sterols by the action of heat. Waterman (1939) found carcinogenic hydrocarbons in food-induced tumors in mice. Beck and Peacock in expts. on rats and mice repeatedly fed heated fats in addition to an adequate basal diet containing sufficient vitamin A discovered in repeatedly heated fats a factor which interfered in some way with the absorption or metabolism of vit. A. They confirmed Roffo''s claim that heated fats cause papillomatosis in the fore-stomach of rats, but no evidence of glandular tumors or of sarcoma was found. Signs of vit. A deficiency appeared. The rat livers contained less Vit. A than those of controls. Rats fed repeatedly heated hydrocarbons in addition to a diet rich in Vit. A (carrot) did not have the tumors or reduction of Vit. A. A substance in repeatedly heated fats interferes with the antimony trichloride reaction, giving a bright red coloration.