A muscarinic cholinergic ligand, N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)-acetamide (Compound BM-5), was shown to act simultaneously as a presynaptic antagonist and as a postsynaptic agonist at peripheral and central muscarinic synapses. In the presence of eserine it enhanced release of [3H]acetylcholine evoked by electrical stimulation in the guinea pig ileum longitudinal muscle myenteric plexus preparation. It also enhanced the release of [3H]acetylcholine evoked by potassium (25 mM) from rat hippocampal slices. It contracted the ileum and stimulated the synthesis of cyclic guanosine 3',5'-monophosphate in rat hippocampal slices and in human lymphocytes in a manner similar to the muscarinic agonist oxotremorine. This effect of BM-5 could be blocked by atropine.