The potency of a series of opioid and non-opioid psychotomimetic drugs to inhibit the specific binding of [3H]PCP and ( + )-[3H]SKF-10,047 to rat cerebral cortical membranes was examined. ( + )-PCMP, the 3-methylpiperidino analog of PCP, was a potent inhibitor of the specific binding of both ligands. All of the other 12 compounds examined, however, displayed a 3-277-fold selectivity for either [3H]PCP or (+)-[3H]SKF-10,047 binding. These results suggest that although these opioid and non-opioid psychotomimetics bind to both sites, most have significantly different affinities. The binding sites for [3H]PCP appear to be distinct from the 'sigma' binding sites labeled with (+)-[3H]SKF-10,047. SKF-10,047 Sigma receptor Phencyclidine Phencyclidine receptor Psychotomimetic activity.