Brains from 4 normal and 4 colchicine-treated rats were studied for the presence of growth hormone-releasing factor (GRF) using an antibody directed against rat hypothalamic GRF (rGRF). Noncolchicine-treated animals showed intense staining in the external layer of the median eminence. Rats pretreated with intraventricular colchicine for 48 h showed localization of GRF-containing cell bodies in the arcuate nucleus, the perifornical area, the lateral basal hypothalamic region and lateral to the ventromedial nucleus and the premammillary nucleus. This pattern of distribution is consistent with the postulated role of GRF in hypothalamic regulation of growth hormone secretion. Our results confirm the predominant localization of GRF perikarya in the arcuate nucleus of the rat which has been noted in studies using antibodies directed against both human pancreas GRF (hpGRF) and rGRF, and demonstrate a unique pattern of rGRF-positive cell bodies elsewhere in the hypothalamus. No rGRF perikarya or processes were seen outside the hypothalamus.