We plan to determine (a) whether some dietary proteins of inferior biological value inhibit the digestion and reutilization of significant quantities of endogenous proteins, and (b) the extent to which this effect explains inferior biological value. Labeled pancreatic enzymes will be infused intraduodenally and the rate and locus of their hydrolysis determined. Conscious rats with biliary and pancreatic fistulae will be used to study the rate of proteolytic enzyme activation and the stability of the digestive enzymes in vivo. The effect of bile and dietary substrate on these processes will be determined. Adaptation of pancreatic hydrolases to changes in diet composition will be studied in the conscious rat with pancreatic and biliary fistulae.