1. The distribution of the messenger RNA (mRNA) encoding the D2 dopamine receptor has been mapped in the monkey brain by in situ hybridization. 2. Using [35S]-labelled riboprobes corresponding to the region of the D2 dopamine receptor spanning the third cytosolic loop and the sixth and seventh transmembrane domains, specific hybridization was observed in a number of neural structures. 3. High levels of mRNA expression were observed in the caudate, putamen, and claustrum. Significant amounts were also identified in the hippocampus, lateral geniculate nucleus, much of the cortex, amygdala, pons, and thalamus. High levels of this mRNA were also visualized in the substantia nigra, likely reflecting autoreceptor synthesis. 4. While the distribution of D2 dopamine receptor mRNA was similar between the monkey and previously published maps in the rat, several differences were noted. 5. These results demonstrate the feasibility of visualizing this mRNA in the primate brain, and suggest that a similar analysis of human postmortem brain material may be possible.