In order to study the effect of the calcium antagonist, verapamil, on glibenclamide stimulated insulin release, nine healthy fasted male volunteers were given 5 mg oral glibenclamide with either 120 mg oral verapamil or placebo in a double-blind crossover manner 1 week apart. Blood was withdrawn at intervals for drug, hormonal and glucose estimations. Concomitant administration of verapamil resulted in higher levels of glibenclamide at each time point (P less than 0.01) suggesting that verapamil interferes with glibenclamide metabolism. However, levels of plasma glucose, C-peptide, insulin and glucagon did not differ between the verapamil and placebo studies.