Peripheral blood from four groups of seven workers from a chemical manufacturing plant in The Netherlands was analyzed for hemoglobin adducts in erythrocytes and for hprt mutants, micronuclei and SCEs in lymphocytes. Group I workers were incidentally exposed to acute high doses of ethylene oxide ranging from 52 to 785 mg/m3. Group II and III workers were chronically exposed to low doses of ethylene oxide for < 5 years or > 15 years respectively. Group IV workers served as unexposed controls and came from the Occupational Health Department. Hemoglobin adduct levels in group I workers were very high and ranged from 1461 to 19913 pmol HOEtVal/g Hb approximately 1 month after the accident. HOEtVal values for group II and III workers fluctuated between 0 and 190 pmol/g Hb corresponding with average EtO exposure levels in the range of < 0.01 and 0.06 mg/m3 EtO. The statistical analysis of the genetic data did not reveal any statistically significant differences between any combination of worker groups. The genetic tests for group I workers were performed on blood samples collected 89-180 days after the incidental exposure. The absence of enhanced frequencies of mutations, micronuclei and SCEs suggests that significant induction of hprt mutations in vivo did not occur and that persistent preclastogenic lesions were not present in significant amounts when the exposed lymphocytes were put in culture to visualize any induced cytogenetic damage. This finding implies that the incidental exposure to high concentrations of EtO did not cause any measurable permanent mutational/cytogenetic damage in exposed lymphocytes.