The present investigation was designed to evaluate the effect of acute and protracted verapamil administration on insulin and glucagon secretion in man. For this purpose, 14 normal subjects received two consecutive glucose pulses (5 g.i.v. in less than 20 sec or 20 g.i.v. in less than 1 min, 7 subjects for each group), 70 or 90 min apart, before and during an infusion of verapamil (160 microgram/min). Seven additional normal subjects received two consecutive arginine pulses (5 g i.v.), 70 min apart. In 14 inpatients with coronary heart disease, we investigated the effect of protracted verapamil administration. Seven of these subjects underwent two oral glucose tolerance tests (100 g) and the other 7 two arginine tests (30 g) before and after a 10-day treatment with verapamil, 240 mg/die p.o. divided into three doses; the last dose, 80 mg, was given orally 1 h before the performance of the post-treatment test. Verapamil significantly inhibited the acute insulin response (AIR, mean change from 3-10 min) to glucose (5 g), as well as the AIR and AGR (acute glucagon response) to arginine (5 g). By contrast, verapamil failed to alter significantly the AIR to the higher glucose pulse. There was no significant change of oral glucose tolerance after verapamil, nor was there a change in insulin response to oral glucose. By contrast, insulin and glucagon responses to arginine infusion were significantly reduced by the drug.