Recently two hypothalamic releasing factors have been isolated, sequenced and synthesized: corticotropin-releasing factor (CRF) from sheep and rat hypothalami; and growth hormone-releasing factor (GH-RF) from tumors in human pancreas (hpGH-RF) and from rat hypothalami (rhGH-RF). Their biological potencies were tested by various laboratories in vivo and in vitro using rat pituitary cell cultures and the pituitary quarters method. In the present study, we investigated the dynamics of the release of pituitary hormones and the interaction between CRF and hGH-RF and several brain peptides in a pituitary cell-superfusion system. A dose-related ACTH release was found when the cells were superfused with different doses of synthetic CRF. Synthetic hGH-RF44, hGH-RF40, hGH-RF1-29 and purified porcine hypothalamic GH-RF caused similar dose-related releases of GH. In this system, we demonstrated interactions between CRF and vasopressin, CRF and SP, hGH-RF and vasopressin and hGH-RF and PHI-27. We conclude that the control of pituitary hormone secretion is a complex process; several factors may interact with each releasing or inhibiting factor to modulate their effects.