The prejunctional actions of a number of Ca 2+ channel antagonists were investigated. Their effects were assessed on both nerve action potential (AP) conduction and neuromuscular transmission in the vas deferens and internal anal sphincter (i.a.s.) of the guinea-pig and in the rat anococcygeus. Nerve APs were recorded extracellularly with a suction electrode and transmitter release measured by intracellular electrical recording of smooth muscle junction potentials and analysis of the overflow of radiolabelled transmitter.