 Hydrolysis of dietary protein may impact their gastrointestinal kinetics and further metabolism. The primary goal of this work was to measure the metabolic fate of intact or hydrolyzed protein using a protein of good nutritional quality, i.e., casein. A second aim of this study was to assess the true ileal digestibility of dietary protein using different methods including the hydrolyzed casein method and to measure its possible effect on endogenous intestinal N losses in humans. 