In order to investigate the effects of bisphenol A (BPA) on immune system in mice we examined the various immunological parameters. After single oral administration of BPA to female ICR mice, the weights of bodies and lymphoid organs, splenic cellularity and hematological parameters were examined on day 2 and 7. Among them WBC and splenic cellularity were slightly decreased on day 2. To assess the effects of BPA on humoral immune responses, splenic IgM plaque forming cell (PFC) and serum IgM were assayed. When BPA was administered after immunization with SRBC, but not before immunization, IgM PFC against SRBC was significantly lowered in a dose dependent manner. Serum IgM level was also decreased on day 4 when high dose (2000 mg/kg) of BPA was administrated after injection of OVA-antigen. The indexes of splenocyte proliferation (SP) to concanavalin A (Con A) and bacterial lipopolysaccharide (LPS) were measured in vitro by MTT assay. At low concentration BPA slightly increased splenocyte proliferation but at higher concentration it showed significant inhibitory effects on cell proliferation. Mitogen-stimulated SP was also determined with spleen cells from BPA treated mice. Con A-induced SP was slightly decreased and LPS-induced SP was especially inhibited at 1000 mg/kg and 2000 mg/kg of BPA. These results indicate that BPA is able to acutly evoke humoral and cell mediated immune suppression in mice.