The present study was designed to test whether chronic neuroleptic treatment, which is known to alter both expression and density of dopamine D2 receptors in striatal regions, has effects upon function and binding level of the cannabinoid CB1 receptor in the basal ganglia by using receptor autoradiography. As predicted, subchronic haloperidol treatment resulted in increased binding of 3H-raclopride and quinpirole-induced guanosine 5′-O-(γ-[35S]thio)triphosphate ([35S]GTPγS) in the striatum when compared to that measured in control animals. This increased D2 receptor binding and function after 3 days washout was normalized after a 2-week washout period. Effect of haloperidol treatment was studied for CB1 receptor binding and CP55,940-stimulated [35S]GTPγS in the striatum, globus pallidus, and substantia nigra. 3[H]CP55,940 binding levels were found in rank order from highest to lowest in substantia nigra > globus pallidus > striatum. Furthermore, subchronic haloperidol treatment resulted in elevated binding levels of 3[H]CP55,940 in the striatum and the substantia nigra and CB1 receptor-stimulated [35S]GTPγS bindings in the substantia nigra after 3 days washout. These increased binding levels were normalized at 1–4 weeks after termination of haloperidol treatment. Haloperidol treatment had no significant effect on CB1 receptor or [35S]GTPγS binding levels in globus pallidus. The results help to elucidate the underlying biochemical mechanism of CB1 receptor supersensitivity after haloperidol treatment. © 2005 Wiley-Liss, Inc.