DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein of Mr = 32,000) mRNA distribution was examined in adult mouse central nervous system by in situ hybridization. In general, DARPP-32 mRNA was found in regions of brain where cells express the dopamine D1 subtype receptor. Cells of the olfactory tubercle, caudate-putamen, and nucleus accumbens had the highest levels of DARPP-32 mRNA, as did choroid plexus and Purkinje cells. Relatively high levels were found in medial habenula and lateral piriform cortex. Moderate levels were seen in cerebral cortex layer VI, medial piriform cortex, lateral entorhinal cortex, tenia tecta, anterior olfactory nucleus, and lateral bed nucleus of the stria terminalis. Low levels were observed in hippocampus, cerebral cortex layers II and III, olfactory bulb, and the nucleus of the lateral olfactory tract. DARPP-32 mRNA levels in the amygdaloid nuclei varied greatly.