Binding and photoaffinity labeling experiments were employed in order to differentiate 1-(1-phenylcyclohexyl)piperidine (PCP) receptor sites in rat brain. Two classes of PCP receptors were characterized and localized: one class binds [3H]-N-[1-(2-thienyl)cyclohexyl] piperidine ([3H]TCP) with high affinity (Kd = 10–15 nM) and the other binds the ligand with a relatively low affinity (Kd = 80–100 nM). The two classes of sites have different patterns of distribution. Forebrain regions are characterized by high-affinity sites (hippocampus > frontal cortex > thalamus > olfactory bulb > hypothalamus), but some parts (e.g., hippocampus, hypothalamus) contain low-affinity sites as well. In the cerebellum only low-affinity sites were detected. Binding sites for [3H]PCP and for its photolabile analogue [3H]azido-PCP showed a regional distribution similar to that of the [3H]TCP sites. The neuroleptic drug haloperidol did not block binding to either the high- or the low-affinity [3H]TCP sites, whereas Ca2+ inhibited binding to both. Photoaffinity labeling of the PCP receptors with [3H]AZ-PCP indicated that five specifically labeled polypeptides of these receptors (Mr 90000, 62000, 49000, 40000, and 33 000) are unevenly distributed in the rat brain. Two of the stereoselectively labeled polypeptides (Mr90000 and 33 000) appear to be associated with the high- and low-affinity [3H]TCP-binding sites; the density of the Mr90000 polypeptide in various brain regions correlates well with the localization of the high-affinity sites, whereas the density of the Mr33 000 polypeptide correlates best with the distribution of the low-affinity sites. The results are compatible with the existence of two classes of PCP receptors in the rat brain, each having a distinct polypeptide that carries the ligand recognition site and has a selective localization in the brain.