In 1941 Kensler, et al observed that the B-vitamin riboflavin protected rats against the potent hepatocar-cinogen aminoazo dyes (1). Ten years later Mueller and Miller showed that this vitamin enzymatically cleaved these dyes to noncarcinogenic metabolites in the liver (2). Further studies in the laboratory of Miller showed enhanced hepatic metabolism of these dyes when rats were fed a practical ingredient type of diet as compared to a more purified diet composed of casein, sugar, corn oil, cellulose, vitamins, and minerals (3).