BACKGROUND: A potent bladder carcinogen for workers in the dye industry, 4-aminobiphenyl (4-ABP), is present in environmental tobacco smoke and has been shown to bond covalently with hemoglobin. PURPOSE: The goal of this study was to examine the relationship between exposure to environmental tobacco smoke and levels of 4-ABP-hemoglobin adducts in nonsmoking pregnant women and to compare adduct levels in those women with levels in smoking pregnant women. METHODS: A questionnaire on smoking and exposure to environmental tobacco smoke was administered to 15 pregnant women who smoked cigarettes and 40 who did not smoke. Exposure was quantified for 1 week with a personal diary and by air sampling with a monitor worn by each woman. The monitor collected nicotine by passive diffusion to a filter treated with sodium bisulfate, and the deposit on the filter was analyzed by gas chromatography. Aliquots of maternal blood and cord blood collected during delivery were analyzed for 4-ABP-hemoglobin adducts by gas chromatography with negative ion chemical ionization mass spectrometry. RESULTS: The mean adduct level in smokers (184 pg of 4-ABP per gram of hemoglobin) was substantially higher than that in nonsmokers (22 pg/g). This difference was statistically significant. Among nonsmokers, the levels of 4-ABP adducts increased significantly with increasing environmental tobacco smoke level (P = .009). Those in the lowest exposure category (< 0.5 micrograms/m3 weekly average nicotine) had median 4-ABP-hemoglobin adduct levels of 15 pg of 4-ABP per gram of hemoglobin, while those in the highest exposure category (> or = 2.0 micrograms/m3) had median levels of 26 pg/g. Nonsmokers in this study had a median adduct level of 20 pg/g, and smokers had a median level of 143 pg/g. CONCLUSIONS: 4-ABP-hemoglobin adduct levels in nonsmokers were 14% of the levels in smokers, which is consistent with findings of 20% in two other studies. Nonsmokers may receive a nontrivial dose of carcinogens from environmental tobacco smoke proportional to their exposure to environmental tobacco smoke. IMPLICATION: The relationship between environmental tobacco smoke exposure and 4-ABP-hemoglobin adduct levels supports epidemiologic evidence that environmental tobacco smoke is carcinogenic to passive smokers.