The results of a study of molecular, cytogenetic, and hematologic effects in ethylene-oxide (75218) exposed female hospital workers were presented. The study group consisted of 36 women employed in nine hospitals in the US, mean age 43.6 years, and 22 women, mean age 29.4 years, employed at a hospital in Mexico. They had experienced cumulative ethylene-oxide exposures of 0 to 32+ parts per million (ppm) hours. On a time weighted average basis, the ethylene-oxide exposures were generally below the OSHA standard of 1ppm. The subjects completed a questionnaire to obtain information on demographic characteristics, occupational history, potential ethylene-oxide exposure, smoking, consumption of caffeinated and alcoholic drinks, and medical history including details on exposure to diagnostic X-rays. Standard hematologic parameters were measured. The hemoglobin was isolated to assess formation of hydroxyethylhemoglobin (HOETHb) adducts. The lymphocytes were harvested to determine sister chromatid exchange (SCE) and micronuclei induction. Significant exposure related increases in HOETHb adduct concentrations and SCE and micronuclei frequencies were seen in the US hospital workers after adjusting for age, cigarette smoking, and other potential confounders. Induction of HOETHb adducts showed an exposure related increase in the Mexican workers. No association between ethylene-oxide exposure and SCE and micronuclei frequency was seen in the Mexican workers. Exposure related decreases in hematocrits, hemoglobin concentrations, and relative neutrophil counts and increases in relative lymphocyte counts were seen in the US workers. No statistically significant changes in the hematologic parameters were seen in the Mexican workers. Multiple linear regression analysis showed a positive exposure relation with relative lymphocyte counts and a negative exposure relation with relative neutrophil counts in the US workers after controlling for confounders. In the Mexican workers, a positive exposure relation was seen with absolute and relative neutrophil counts. The authors conclude that exposure to ethylene- oxide at concentrations below the OSHA standard can result in molecular and cytogenetic changes.