Light microscopic autoradiographical localization of drug and neurotransmitter receptors provides investigators with a tool to determine the sites of drug action with a high degree of anatomical resolution. In the cortex, where there is a distinct laminar organization, the differential distribution of receptors can be determined. We have found that differences in the density of specific receptors exist between layers of the cerebral cortex. Our observations include the localization of muscarinic cholinergic, benzodiazepine, opiate, neurotensin, histamine-H1, alpha-adrenergic, beta-adrenergic, and high-affinity GABA receptors in the cerebral cortex. Of this list of neurotransmitters only significant concentrations of benzodiazepine, GABA, and beta-adrenergic receptors were found in the cerebellar cortex. Receptor localizations such as these can be coupled with information from immunohistochemical studies to provide the basis for future experimentation in order to define neurotransmitter-specific pathways in the cerebral and cerebellar cortices.