Gas chromatographic-mass spectrometric analysis of profiles of low molecular weight volatile organic constituents obtained from cord blood and maternal blood samples collected at birth reflect transplacentally acquired compounds. The transplacental passage of halogenated hydrocarbons, plastic components, and abnormal accumulations of compounds have been demonstrated. In the 11 paired cord blood-maternal blood samples analyzed, the relative amounts of constituents in cord blood closely correspond to those quantities present in the maternal blood. However, some of the over 100 components are present in the cord blood in significantly higher concentrations than in the maternal blood, suggesting a possible selective one-way transfer of certain constituents into the fetus. Benzene, carbon tetrachloride, and chloroform are present in quantities equal to or greater than in maternal blood. In one infant with a lumbosacral meningomyelocele abnormally high concentrations of acetone, other components, and the food preservative 2, 6-di-tert-butyl-4-methylphenol (BHT) were identified.