Bisphenol A (BPA) is one of the most important endocrine disrupting chemicals. Epoxy resins and polycarbonates are frequently manufactured using this compound. Enzyme histochemical techniques not only can be used to evaluate the general status of the immune system but also are used to determine the functional situation of the lymphocytes. Immunocompetent T-lymphocytes in certain animal species are characterized by the presence of ANAE (Alpha Naphthyl Acetate Esterase). The purpose of this study is to determine the effects of BPA on the proportions of ANAE positive peripheral blood lymphocytes (PBL) in rats. A total of 40 rats were used. Forty animals were randomly assigned to five experimental groups (n = 8 per group): control, vehicle-control, BPA-5, BPA-50, and BPA-500. The BPA- 5, BPA-50 and BPA-500 groups were given 5, 50, and 500 ?g/kg body weights/day, respectively. At the end of the 8 weeks, peripheral blood samples were obtained from the rats and blood smears were prepared for ANAE demonstration. On each smear, two-hundred lymphocytes were counted for the determining of the percentages of ANAE-positive lymphocyte percentages. The proportions of ANAE positivity were found as 43.37%, 36.50%, 32.62%, 31.37% and 30.75% respectively. It was determined that the differences of the proportions of ANAE positive PBL between the groups were statistically important (p<0.01). It was concluded that BPA had immunotoxic and/or immunosuppressive effect of PBL, and it might cause functional failure of lymphocytes affecting their enzymatic activity.