The effects of neonatal administration of estrogenic agents on rat reproductive organs were examined. Either bisphenol A (BPA; 0.25, 1, or 4mg/pup) or 10 micro g 17beta-estradiol (E(2)) was given subcutaneously to Sprague-Dawley female rats during the neonatal period from post-natal day (PND) 0 to 9. Animals ovariectomized at 80 days were given subcutaneous injections of 1 micro g/kg E(2) for 3 days from PND 94 to 96. Clefts in the clitoris, early vaginal opening, irregular estrous cycles, a decrease in the area occupied by the corpora lutea (CL) in the ovary, and multiple cystic follicles in the ovary were found in the animals treated neonatally with 1mg BPA. Uterine fluid weight measured after E(2) treatment on PND 94-96 was less than controls. In addition to these abnormalities, unusual body weight gains, persistent vaginal cornification, and lack of CL were observed in females treated neonatally with 4mg BPA. The ovary weight on PND 80 and uterine fluid weight measured after E(2) treatment on PND 94-96 were less than controls for the 4mg BPA group. Neonatal treatment with 10 micro g E(2) induced similar abnormalities as found in the 4mg BPA group. These results show that BPA when given during the neonatal period caused changes in female reproductive organs.