In addition to their role as lymphocyte messengers, cytokines also act at the anterior pituitary gland as autocrine or paracrine regulators of anterior pituitary function. As a cellular and molecular basis for this latter role, receptors for interleukin (IL)-1, IL-2 and IL-6 have been demonstrated in the pituitary of several species, as the endogenous production of the homologous cytokines. Additional cytokines are synthesized in or alter the function of the pituitary. IL-1, IL-2 and IL-6 regulate not only the secretion of pituitary hormones, but also the growth and proliferation of pituitary cells. This latter action suggests that intrinsically produced cytokines play a role in the pathogenesis of pituitary adenomas. Cytokines thus constitute a complex autocrine or paracrine network that contributes to the regulation of anterior pituitary physiology and pathophysiology.