Using a specific monoclonal antibody (mAb) recognizing the rat interleukin-2 receptor (IL-2R) and immunocytochemical techniques, we examined the expression of IL-2R in rat anterior pituitary and adrenal cells in vitro. IL-2R immunoreactivity was seen in a variety types of cells in both the pituitary and adrenals. Under the condition to detect the IL-2R-like immunoreactivity, we found that overnight preincubation with IL-2 enhanced the immunostaining in these cells. Moreover, co-incubation of the cells with dexamethasone attenuated the effect of IL-2 on the IL-2R-like immunostaining. These findings indicate that IL-2R expression in the pituitary and adrenal cells is influenced by IL-2 and glucocorticoid, and support the hypothesis that IL-2 is an immunomediator affecting the pituitary and the adrenal function.