The existence of a growth hormone-releasing hormone (GHRH)-containing local neuronal network in the arcuate nucleus of the rat has been established on the basis of light and electron microscopic immunohistochemistry. GHRH-immunostained nerve terminals were demonstrated in synaptic contact with GHRH-immunoreactive dendrites and perikarya. These neuronal circuits may allow arcuate GHRH neurons to operate synchronously, or may provide morphological evidence for the existence of a neuronal ultrashort feedback mechanism for regulating GHRH release in the hypothalamo-hypophyseal system.