Phenoxybenzamine, α-adrenoreceptor blocking agent, produced the potentiation of the relaxing response of taenia coli to transmural stimulation. This potentiation effect was prevented in the presence of atropine. Moreover, the relaxing response caused by nicotine was abolished by phenoxybenzamine. These results imply that phenoxybenzamine has blocking actions on the muscarinic receptor and possibly on the nicotinic receptor, as well as the adrenergic α-receptor.