The effect of vasoactive intestinal peptide (VIP) on the release of prolactin (PRL), gonadotropins (LH and FSH), growth hormone (GH) and corticotropin (ACTH) was studied using purified rat anterior pituitary cells obtained by means of velocity sedimentation at unit gravity. VIP, at concentrations ranging from 10–10 to 10–7M, stimulated PRL secretion in a dose-dependent manner with an ED50 of 2 nM and a maximal response of 530% of control values. In contrast, similar concentrations of VIP did not affect the release of either LH, FSH, GH or ACTH from the corresponding enriched cell populations. Addition of dexamethasone (10–9M) to both preincubation and incubation medium of PRL cells completely inhibited VIP-induced PRL release. The present results further support the hypothesis that VIP is of physiological importance in the control of PRL secretion and demonstrate that corticosteroids can modify the responsiveness of PRL cells t