The relationships between proopiocortin neurons have been studied in the rat hypothalamic arcuate nucleus by immunocytochemistry. At the light microscopic level, contacts between immunostained endings and cell bodies or dendrites were frequently observed. At the electron microscopic level, stained nerve terminals were seen making symmetrical synaptic contacts with labeled dendrites and cell bodies. These observations are the first indication that neurons producing the same peptides can have contacts between themselves. This provides morphological evidence for autoregulation of neuropeptide systems.