Binding of a novel radioligand, [3H]3-OH-PCP (1(1(3-hydroxyphenyl) cyclohexyl)piperidine), to N-methyl-D-aspartate (NMDA) receptor-coupled and -uncoupled PCP sites was investigated in the rat brain. The highest densities of [3H]3-OH-PCP binding were observed in the hippocampal formation, notably in the stratum radiatum and oriens of CA1 region, and dentate gyrus. There were relatively high levels of binding in the olfactory system, superficial layer of cortices, the amygdala and the thalamus. In contrast, lower levels of binding were found in the globus pallidus, cerebellum, and brain stem, except for the superior colliculus. These findings demonstrate that [3H]3-OH-PCP binds to discrete regions within the rat brain. Its distribution is consistent with autoradiographic localization of [3H]TCP and [3H]MK-801 binding sites in the rat brain, suggesting that [3H]3-OH-PCP binds to NMDA/PCP ion-channel complexes in preference to sigma sites.