To determine whether or not bisphenol A affects the immune system, female ICR mice were treated bisphenol A(BPA) orally at the doses of 100, 500 and 1,000 mg/kg for 30 consecutive days. Four days before enumerating plaque-forming cells(PFCs) mice were immunized intraperitoneally with sheep red blood cells(SRBCs). The spleen cellularity and PFC/spleen were significantly reduced by 30-day exposure to BPA(1,000 mg/kg/day), but the PFC/10^6 spleen cells was slightly decreased. When splenocytes isolated from the mice exposed to BPA for 30 days were cultured in the presence of LPS, Con A or PHA with IL-2, the lymphocyte proliferation ex vivo was not significantly suppressed by BPA. Our present results indicated that 30-day exposure of mice to BPA might have mild immunotoxic potential.