Women comprise the majority of workers exposed to ethylene oxide during sterilization of medical instruments and supplies. This article evaluates molecular, cytogenetic, and hematologic effects of ethylene oxide on 68 women workers employed in nine hospitals in the United States and one hospital in Mexico. Workers were classified by three exposure categories: none (0), low (> 0-32 ppm-hrs), and high (> 32 ppm-hrs). Hematologic effects were evaluated using complete blood count with differential, which has been questioned as a test for screening ethylene oxide-exposed workers. A statistically significant decrease in hematocrit (n = 0.02) and hemoglobin (P = 0.03) levels, an increase in lymphocyte percentages (P = 0.04), and a relative decrease in neutrophil percentages (P = 0.03) with exposure were observed in US workers. The absolute number of lymphocytes, however, showed no relationship with exposure. No statistically significant results were seen for Mexican workers, although hematocrit decreased with exposure. An exposure-response relationship for the percentage for lymphocytes (positive) and neutrophils (negative) in US subjects and for neutrophils (positive) in Mexican subjects was seen. No overall relation with exposure was observed for total number of white cells. Molecular and cytogenetic results are also reported for the 68 women, who constitute a subgroup from a previous report. US women workers showed a statistically significant exposure-response relationship for ethylene oxide and hemoglobin adducts (P = 0.0002) and sister chromatid exchanges (P = 0.001). For micronuclei, the difference (P = 0.02) between low and high exposure was statistically significant. In Mexican workers, an exposure-response relationship was observed (P = 0.002) for hemoglobin adducts but not for sister chromatid exchanges or micronuclei.