Rats were fed on diets containing different levels of protein. Severe vitamin B6-deficiency was observed in rats receiving a high protein, vitamin B6-deficient diet. The growth of these rats was inhibited within a week and their liver transaminase activities were markedly decreased. Rats receiving a low protein diet with or without vitamin B6 grew normally during the experimental period and only slight decreases in the liver transaminase activities were observed. Vitamin B6-depletion was found to decrease induction of liver transaminases [L-alanine: 2-oxoglutarate amino-transferase, EC 2. 6.1. 2, and L-aspartate: 2-oxoglutarate ami not ransferase, EC 2. 6.1.1] by cortisol. A high protein, vitamin B6-deficient diet induced fatty liver with increased levels of glycerides and cholesterol.