Prolactin (PRL)-releasing peptide (PrRP) is a recently discovered hypothalamic peptide possessing a specific stimulatory action on PRL secretion. In this study, we examined whether PrRP plays a role in mediating ether stress- and suckling-induced PRL secretion in rats through administering anti-PrRP antisera intracerebroventricularly. For comparison, we also tested the effect of anti-vasoactive intestinal peptide (VIP) antisera on the hormonal responses, since VIP is another candidate for a physiological PRL-releasing factor. The immunoneutralization of VIP, but not of PrRP, led to a significant suppression of PRL responses to both ether and suckling. These results suggest that PrRP may not play a significant role, or at least play a much weaker role than VIP, in mediating PRL release induced by ether stress and suckling in the rat.