Corticotropin releasing factor (CRF) both stimulates ACTH secretion from the pituitary and inhibits secretion of growth hormone (GH) in adult rats through actions in the CNS. The purpose of the present study was to evaluate these pituitary and central actions of CRF in neonatal rats, in which the hypothalamo- pituitary adrenal (HPA) axis is relatively hypo-functional. The results of this study show that central or peripheral administration of CRF evokes a marked dose-related rise in serum corticosterone in 6-day old rats. The same doses of CRF stimulate, rather than inhibit GH secretion. These results suggest that CRF has unique central actions early in ontogeny.