The psychotomimetic analgesic phencyclidine (PCP), which binds to a high affinity site on the neuronal N-methyl-D-aspartate (NMDA)-sensitive glutamate receptor, has previously been found to bind to platelets with high affinity and to specifically delay the onset of epinephrine-stimulated platelet aggregation (Jamieson et al. (1992) Biochem. J. 285, 35-39). We have now shown that the rank order of binding affinities of 14 synthetic PCP analogs at the high affinity binding site on platelets does not parallel the rank order of their affinities in binding to rat brain membranes, indicating that the high affinity PCP binding sites in platelets is distinct from the neuronal NMDA receptor. The order of potency of six of these analogs in delaying the onset of epinephrine-stimulated platelet aggregation also did not parallel the rank order of their binding affinities for platelet or brain binding sites. These data indicate that the ability of PCP analogs to inhibit epinephrine-stimulated aggregation is not related to their ability to bind to the high affinity platelet PCP binding site. Furthermore, (+)MK-801, which binds to the same high affinity binding site in neurons as does PCP, failed to inhibit epinephrine-stimulated platelet aggregation, further suggesting that the site at which PCP acts in platelets is not related to the NMDA-type glutamate receptor. Further studies showed that 5-HT2 receptors and effects on platelet secretion are not involved in PCP-mediated inhibition of epinephrine-induced platelet aggregation.