In this study, the clinical use of iv verapamil [0. 1 mg/kg] in patients receiving repeated iv fractional doses of pancuronium bromide prolonged the duration of skeletal muscle relaxation with consequent reductionofthetotal dosage of pancuronium bromide. This interaction was noticed in patients who received verapamil to abolish supraventricular tachycardia occurring during operative procedures in open heart surgery. The study of the interaction between verapamil and skeletalmusclerelaxants [pancuronium and succinylcholine] in experimental animals evidenced that verapamil per se in a 100 mug/kg iv dose was devoid of any skeletal muscle relaxant effect of the gastrocne miussciaticne rvepreparation. Administrationof pancuronium [8 mug/kg] one hour after verapamil resulted in two folds increase in intensity of muscle relaxation along with 1. 5 folds prolongation in duration of recovery compared with that before verapamil. This action is the result of inhibition of conductance of the presynaptic membrane to calcium, thus affecting transmitter release and block its action on postsynaptic membrane. In contrast, a less marked degree of potentiated increase by verapamil of the intensity of neuromuscular block with no simultaneous delay in recovery was encountered in the case of succinylcholine; this was explained on the basis of hyperkalemia produced by succinylcholine counteracting blockade by verapamil the outward K+ efflux during repolarizationim