Hemoglobin (Hb) and albumin (Alb) adducts of the benzene metabolites benzene oxide (BO) and 1,4-benzoquinone (1,4-BQ) were analyzed by gas chromatography-mass spectrometry in 43 exposed workers and 44 unexposed controls from Shanghai, China, as part of a larger cross-sectional study of benzene biomarkers. When subjects were divided into controls (n = 44) and workers exposed to </=31 ppm (n = 21) and >31 ppm (n = 22) of benzene, median 1,4-BQ-Alb adducts were 2110, 5850, and 13,800 pmol/g Alb, respectively (correlation with exposure: Spearman r = 0.762; P < 0.0001); median BO-Alb adducts were 106, 417, and 2400 pmol/g Alb, respectively (Spearman r = 0.877; P < 0.0001); and median BO-Hb adducts were 37.1, 50.5, and 136 pmol/g Hb, respectively (Spearman r = 0.757; P < 0.0001). To our knowledge, this is the first observation that adducts of 1,4-BQ are significantly correlated with benzene exposure. When compared on an individual basis, Alb adducts of 1,4-BQ and BO and Hb adducts of BO were highly correlated with each other and with urinary phenol and hydroquinone (P < 0.0001 for all of the comparisons). Although detectable in the assays, Hb adducts of 1,4-BQ and both Hb and Alb adducts of 1,2-BQ produced erratic results and are not reported. Interestingly, cigarette smoking increased Alb adducts of 1,4-BQ but not of BO, suggesting that benzene from cigarette smoke was not the primary contributor to the 1,4-BQ adducts.