Summary Human banked blood stored in several anti-coagulant-containing solutions for varying periods was administered to mongrel dogs with portacaval shunts. The magnitude of rise in the animal's blood ammonia was not significantly affected by the free ammonia content of the blood administered. Curves for systemic blood ammonia produced by this regimen were compared with curves obtained when isonitrogenous amounts of casein or casein hydrolysate were administered. In view of the almost identical patterns of rise in blood ammonia obtained when whole blood or casein hydrolysate was fed and the lack of valid differences in mean hourly levels of blood ammonia between dogs fed blood or whole casein, casein feeding does not appear to hold great promise as a method for prevention of hyperammonemia in patients with liver disease and associated meat intoxication. The somewhat lower values for blood ammonia observed after feeding of whole casein as compared with whole blood may be explained on the basis of a slower rate of proteolysis and, thus, delayed absorption of the amino acids and ammonia released from whole casein.