We examined differences in pancreatic growth, enzyme content and enzyme concentration between rats fed diets containing normal (2.49 g nitrogen/kg diet) or high (7.46 g nitrogen/kg diet) levels of an amino acid mixture and those in rats fed diets containing normal and high levels of casein for 11 d. Rats fed these diets were injected with a potent cholecystokinin antagonist, MK-329 (2.5 mg/kg body wt.d) or with vehicle only. Pancreatic contents (units in pancreas per 100 g body wt) of protein, trypsinogen and chymotrypsinogen were greater in rats fed a high amino acid diet compared with those in rats fed a normal amino acid diet. Proportionate increases in protein and the serine proteases in pancreata of the high amino acid group relative to those of the normal amino acid group were comparable to those of the high casein group relative to the normal casein group. The pancreatic protease concentrations (units/g pancreas) of rats fed the high casein diet and treated with MK-329 were lower than in rats fed high casein but not treated with MK-329. This difference was not observed in rats fed the high amino acid diet. These results demonstrate that pancreatic growth and proteases are induced by dietary amino acids in rats, and the stimulatory effects of amino acids on exocrine pancreas do not depend on cholecystokinin.