In an experiment involving the feeding of different protein sources to one-week old chickens, no statistically significant differences occurred in the amino acid content of the chicken carcasses despite considerable differences in body mass changes as a result of the dissimilar diets fed. Highly significant correlation coefficients were obtained between body water content and the content of essential amino acids in the carcass. Carcass amino acid analysis could therefore, under set conditions, be calculated from the body water content by using predetermined regression equations. Net amino acid utilization studies indicated that lysine is the first-limiting amino acid in sunflower meal and that isoleucine is first-limiting in fishmeal. Sixty-four % of the isoleucine in fish meal and 75% of the lysine in sunflower meal was utilized by the chickens for tissue growth.