To assess human exposure to bisphenol A (BPA) over a 10-year period, BPA concentrations in maternal serum (MS) and amniotic fluid (AF) obtained at early second trimester were determined. ELISA was used to measure BPA in 200 MS/AF pairs in women carrying fetuses with normal karyotypes (Group I) and in 48 pairs with abnormal karyotypes (Group II). In Group I, BPA concentrations in AF (median: 0.26 ng/ml) were lower (P<0.01) than in MS (2.24 ng/ml). Over a 10-year period, yearly BPA concentrations in MS decreased from 5.62 to 0.99 ng/ml (P<0.001). Eight of the Group I AF samples had relatively high concentrations of BPA (2.80-5.62 ng/ml). In Group II, BPA concentrations in AF (0 ng/ml) were lower (P<0.01) than in MS (2.97 ng/ml). MS BPA concentrations in Group II were higher (P<0.01) than in Group I.