Cord serum and maternal milk levels of polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) were examined in relation to maternal serum levels. Maternal serum levels were significantly higher than cord serum levels for both types of compounds. Placental passage was indicated by significant maternal to cord serum correlations for both PCBs (r = .42) and PBBs (r = .81). Correlations between maternal serum and milk levels were similar. Higher PBB correlations were probably due to greater reliability in the measurement of PBB levels in serum and milk.