Apamin, a peptide of bee venom, was shown to inhibit the relaxant responses of guinea-pig taenia caeci to ATP, noradrenaline, adenosine and, less effectively, to stimulation of noradrenergic inhibitory nerves. Thus apamin acts nonspecifically and, contrary to the suggestion of Vladimirova and Shuba (1978), the fact that inhibitory responses due to nerve stimulation and ATP are blocked by the toxin does not allow conclusions as to the possible transmitter role of ATP in these nerves.