Leptin is a cytokine produced by white adipose tissue that circulates in direct proportion to adiposity and is an important signal of energy balance. Leptin inhibits food intake in rodents by inhibiting the orexigenic neuropetides neuropeptide Y (NPY) and agouti regulated peptide (AgRP) and stimulating the anorexigenic neuropeptides α-melanocyte-stimulating hormone (α-MSH) and cocaine-amphetamine-regulated transcript (CART). In order to extend our understanding of neuroendocrine regulation of appetite in the primate, we determined the effect of a metabolic challenge on CART, NPY, and leptin receptor (Ob-R) messenger ribonucleic acid (mRNA) in the nonhuman primate (NHP) hypothalamus. Ten adult female rhesus monkeys were either maintained on a regular diet or fasted for two days before euthanasia. CART, NPY, and Ob-R mRNA were measured by in situ hybridization histochemistry (ISHH). A 2-day fast decreased CART expression in the ARC, increased NPY gene expression in the supraoptic nucleus (SON) and paraventricular nucleus (PVN), and increased Ob-R expression in the ventromedial nucleus (VMN). This is the first report that fasting inhibits CART expression and stimulates Ob-R expression in monkeys. Increased NPY expression in the SON and PVN, but not the ARC of fasted monkeys also is novel. With some exceptions, our observations are confirmatory of findings in rodent studies. Similarities in the neuroendocrine responses to a metabolic challenge in monkeys and rodents support extending existing hypotheses of neuroendocrine control of energy homeostasis to primates.