The atypical neuroleptic clozapine has clinical and behavioral properties that differ not only from the typical compounds, but also from atypical ones. It interacts with the dopaminergic systems, but also produces effects on the serotoninergic, GABA-ergic, cholinergic systems. In spite of the amount of papers devoted to its study, the profile of the neurochemical action of this drug is still confuse. In this paper we investigated the DA2-, opiate- and benzodiazepine-receptor modifications induced by the long term (21 days) treatment with clozapine 20 mg/kg/day in the rat brain. We found a decrease of DA2 receptor density in the target areas of the mesolimbocortical system (ventral n. caudate-putamen, cerebral cortex except for the anterior cingulate at the most anterior level and the n. accumbens) and a decrease of opiate and benzodiazepine receptors in the cerebral cortex and in the olfactory tubercle. Opiate receptors increase in the patches of the striatum. We also compared these effects with those produced by long-term (21 days), low-dosage (0.5 mg/kg day) haloperidol.