Study subjects are nonsmoking Dominican and African-American women residing in Washington Heights, Central Harlem, and the South Bronx, New York, who delivered at New York Presbyterian Medical Center, Harlem Hospital, or their satellite clinics since February 1998, as previously described (Perera et al. 2003 (link)) (Table 1). Subjects signed a consent form approved by the Columbia University institutional review board. Race/ethnicity was self-identified. Subjects were interviewed using a questionnaire to elicit environmental and health histories, including exposure to tobacco smoke at home or work and dietary ingestion of PAHs via smoked, fried, broiled, barbecued, and grilled foods. Subjects included in the present analysis are those with available PAH-DNA adduct data for both mother and child. Not all subjects in the ongoing parent study (n = 474) had adduct data available because assays are ongoing and in some cases the amount of DNA was inadequate for analysis. However, the present subset is representative of the larger study cohort in that there were no significant differences between the present subset and the overall cohort with respect to any of the demographic and exposure variables shown in Table 1. Maternal blood (30–35 mL) was collected within 1 day postpartum, and umbilical cord blood (30–60 mL) was collected at delivery (Perera et al. 2003 (link)). Samples were transported to the laboratory immediately after collection. The buffy coat, packed red blood cells, and plasma were separated and stored at −70°C. BaP-DNA adducts in extracted WBC DNA were analyzed using the HPLC–fluorescence method of Alexandrov et al. (1992) (link), which detects BaP tetraols. The assay gives zero values when unexposed calf thymus DNA is tested (D. Tang, personal communication). The method has a coefficient of variation of 12% and a lower limit of detection of 0.25 adducts per 108 nucleotides. HPLC analysis of DNA samples for BaP-DNA adducts was performed in batches, with 18-paired maternal and newborn samples in the same batch. A portion of each sample was shipped to the Centers for Disease Control and Prevention for analysis of cotinine using HPLC atmospheric-pressure ionization tandem mass spectrometry, as previously described (Bernert et al. 2000 (link)). Current data on annual average ambient concentrations of BaP in New York City are not available. However, outdoor 24-hr average BaP concentrations measured in U.S. urban areas have generally been in the range of 0.5–4 ng/m3 in recent years (U.S. EPA 1990 ). Personal air monitoring of the New York City mothers for 48 hr during pregnancy provided data on PAHs, including BaP (Perera et al. 2003 (link)). For the first 344 subjects analyzed, the average personal BaP concentration was 0.5 ng/m3 (range, 0.02–6.44). This may be an overestimate of mean ambient exposure because personal monitoring can also reflect indoor sources such as ETS. We estimate that the ambient BaP exposure of the New York City cohort, and by inference their exposure to other related PAHs, was at least 6- to 30-fold lower than that of the Polish cohort (0.5 vs. 3–15 ng/m3).