In rodents, D1 dopamine receptors are expressed in the suprachiasmatic nucleus and are believed to play important roles in regulating circadian rhythms. It is not currently known if the primate circadian system can be influenced by dopaminergic agents, which have broad clinical use. To determine if dopamine receptors can potentially influence primate circadian function, we examined the expression of D1 dopamine receptors in the anterior hypothalamus of ring-tailed macaques (Macaca nemestrema), baboons (Papio sp.), and humans. Because D5 dopamine receptors also stimulate adenylyl cyclase activity, D5 dopamine receptor expression was studied as well. We used [ 125 I]SCH 23982, which binds to D1 and D5 dopamine receptors, and labeling of the suprachiasmatic (SCN), supraoptic (SON), and paraventricular (PVN) nuclei was detectable in each species. In situ hybridization studies revealed differential expression of D1 and D5 dopamine receptor mRNA in the hypothalamus. D1 dopamine receptor mRNA was expressed in the SCN, SON, and PVN. By contrast, D5 dopamine receptor mRNA was expressed only in the SON and PVN of baboons and humans. Injection of the D1/D5 dopamine receptor agonist SKF 38393 at night increased the uptake of 2-deoxy-D-[ 14 C]glucose in the SCN, SON, and PVN of newborn baboons. By contrast, c-fos mRNA expression was induced in the SON and PVN, but not in the SCN. These data show that D1 and D5 dopamine receptors are present in the hypothalamus of primates and show that activation of these receptors acutely influences SCN, SON, and PVN activity.