The purpose of this study was to examine the effects of alprazolam on the response of murine immune cells. Splenic cells of young BALB/c mice were first cultured with an optimum dose of various mitogens in the presence or absence of varying doses of alprazolam to assess effects of alprazolam on concanavalin A (Con A)-induced T-cell proliferation, bacterial lipopolysaccharide (LPS)-induced B-cell proliferation, and production of interleukin 2 (IL2). Then, peritoneal adherent cells (macrophages) from young BALB/c mice were cultured with an optimum dose of LPS in the presence or absence of alprazolam to assess the effects of alprazolam on the ability of peritoneal adherent cells to produce interleukin 1 (IL1) and tumor necrosis factor (TNF). The results of this study clearly demonstrated that alprazolam is a potent immunosuppressive agent that can inhibit the proliferative responses of both B- and T-cells to LPS and Con A, respectively. It also can reduce production of IL2 by splenic T-cells and production of both IL1 and TNF by peritoneal macrophages. Furthermore, it was also shown that (a) the magnitude of suppression of T-cell proliferation and of IL2 production occurs in a dose-dependent manner and (b) B-cells are more vulnerable than T-cells to the effect of alprazolam.