The effect of phenformin on the exocrine function of the pancreas was studied in thirteen healthy subjects. Pancreatic exocrine secretion was stimulated by intraduodenal infusion of 100 ml. of a 0.1 N hydrochloric acid solution and, after fifty minutes, intravenous injection of 1 U. secretin per kilogram of body weight. At the same time serum insulin level was determined by a radioimmunologic method. In each subject the test was performed twice; the first test provided control values, and the second was preceded by treatment with phenformin. Administration of the antidiabetic biguanide markedly reduced the basal secretion rate and its amylase content and also inhibited the increase in secretion normally caused by either intraduodenal infusion of a HCI solution or injection of secretin. In these healthy subjects, intraduodenal infusion of a HCI solution produced a smaller increase in insulin secretion than did intravenous injection of secretin. Previous phenformin treatment largely eliminated the increase in insulinemia after intraduodenal infusion of a HCI solution, whereas it failed to affect the increase in insulinemia after secretin injection. The clinical significance of these observations is discussed.

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