The distribution of mRNA coding for the D2 dopamine receptor was studied in the rat brain by in situ hybridization. A cDNA probe corresponding to the putative third cytosolic loop and sixth and seventh transmembrane domains of the rat D2 receptor was used to generate an 33S-labeled riboprobe to hybridize to D2 receptor mRNA. D2 mRNA was found both in dopamine projection fields in an regions associated with dopamine-containing cell bodies, suggesting both postsynaptic and presynaptic autoreceptor localization. Highest concentrations of D2 mRNA were found in neostriatum, olfactory tubercle, substantia nitra, ventral tegmental area and the nucleus accumbens. This distribution is consistent with those reported with D2 receptor autoradiography.