OBJECTIVE To find out if the capacity to secrete insulin and glucagon was affected by pancreatectomy. Insulin and glucagon secretion was measured before and three months after subtotal pancreatectomy. METHODS Open study. METHODS University hospital. METHODS Five patients who each underwent removal of roughly 85% of the pancreas for cancer. METHODS Arginine 5 g given intravenously during glucose infusions that were varied in strength to give blood glucose concentrations of about 5, 15, and 28 mmol/l. METHODS Fasting concentrations of glucose, insulin, and glucagon; and effect of arginine on insulin and glucagon secretion at the different blood glucose concentrations. RESULTS Fasting concentrations of glucose in blood and insulin and glucagon in plasma were not significantly affected by the operation, but arginine-induced secretion of insulin and glucagon were severely impaired. The mean (SEM) insulin response to arginine was reduced from 316 (101) to 129 (29) pmol/l (p < 0.05) and when the patients were at the most hyperglycaemic from 1292 (316) to 474 (115) pmol/l (p < 0.05). The ratio of the change in response of insulin to blood glucose concentrations was also reduced (from 76.8 (25.9) to 27.9 (8.6) pmol/l/mmol/l) (p < 0.01). The plasma glucagon response to arginine was also reduced, by 40% at 5 and 15 mmol/l of glucose, and by 80% at 28 mmol/l glucose (p < 0.05). CONCLUSIONS Though diabetes does not usually develop after subtotal pancreatectomy, the capacity to secrete insulin and glucagon was considerably reduced.