Interleukin-6 (IL-6), a cytokine produced by inflammatory reactions, was found to stimulate PRL, GH and LH release from anterior pituitary cells at concentrations similar to those which affected lymphocyte mitogenesis. Perifused pituitary cells responded to IL-6 with prompt increases in hormone release that declined rapidly following cessation of exposure. Dopamine (DA) attenuated IL6-induced PRL release. In addition, IL-6 potentiated both GHRF- and TRH-induced hormone release without an affect on intracellular cAMP. These data demonstrate a new biological activity for IL-6 and provide evidence for immune system regulation of anterior pituitary hormone release.