The effect of SMS 201-995 on pancreatic exocrine function was studied. The SMS 201-995 was administered to a patient with an artificial external pancreatic fistula following pancreaticoduodenectomy. Variations in pancreatic exocrine function were assessed by determining the volume and components of the fistula fluid during the following periods: 5 d prior to SMS 201-995 administration, for 5 d during actual administration, and for 5 d after it had been discontinued. The SMS 201-995 was administered by subcutaneous injection of 100 micrograms every 12 h for the first 2 d and then 100 micrograms every 6 h for 3 d. This experiment demonstrated that SMS 201-995 has a strong inhibitory effect on pancreatic exocrine function, markedly reducing the amount of fistula fluid and the production of amylase, total protein, and bicarbonate.