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Ethylene oxide (EtO), an important industrial chemical intermediate and sterilant, is classified as a human carcinogen. Occupational EtO exposure in many countries is regulated at 1 ppm (8‐hr TWA), but levels of EtO‐DNA adducts in humans with low occupational EtO exposures have not been reported.We examined the formation of N7‐(2′‐hydroxyethyl)guanine (N7‐HEG), a major DNA adduct of EtO, in 58 EtO‐exposed sterilizer operators and six nonexposed workers from ten hospitals. N7‐HEG was quantified in granulocyte DNA (0.1–11.5 µg) by a highly sensitive and specific gas chromatography‐electron capture‐mass spectrometry method. Cumulative exposure to EtO (ppm‐hour) was estimated during the 4‐month period before the collection of blood samples.There was considerable inter‐individual variability in the levels of N7‐HEG with a range of 1.6–241.3 adducts/107 nucleotides. The mean levels in the nonexposed, low (≤32 ppm‐hour), and high (>32 ppm‐hour) EtO‐exposure groups were 3.8, 16.3, and 20.3 adducts/107 nucleotides, respectively, after the adjustment for cigarette smoking and other potential confounders, but the differences were not statistically significant.This study has demonstrated for the first time, detectable levels of N7‐HEG adducts in granulocytes of hospital workers with EtO exposures at levels less than the current U.S. standard of 1 ppm (8‐hr TWA). A nonsignificant increase in adduct levels with increasing EtO exposure indicates that further studies of EtO‐exposed workers are needed to clarify the relationship between EtO exposure and N7‐HEG adduct formation. Am. J. Ind. Med. 2007. © 2007 Wiley‐Liss, Inc. [ABSTRACT FROM AUTHOR]