The urinary output of trypsin, chymotrypsin, elastase, and amylase by rats with a pancreas transplant and bladder drainage was determined after injection with cholecystokinin (CCK) or by feeding diets containing high (raw soy flour) or low (heated soy flour) trypsin inhibitor activity. The injection of CCK produced a significant increase in the urinary output of all four enzymes. Rats were fed heated or raw soy flour in three consecutive 10-day periods in the following sequence: period 1, heated soy flour; period 2, raw soy flour; period 3, heated soy flour. Replacing heated soy flour in period 1 with raw soy flour in period 2 caused a significant increase in the output of the four enzymes. Subsequent feeding with heated soy flour in period 3 resulted in a reduction in the output of trypsin, chymotrypsin, and elastase to levels that were not significantly different from that observed in period 1. Although amylase output was also reduced in period 3, it did not return to the level noted in period 1. These results are consistent with the roles that CCK and trypsin inhibitors are believed to play in the negative feedback control of pancreatic exocrine function. A similar approach might be employed with humans who have undergone a pancreas transplant with bladder drainage.