To evaluate the effect of exposure pattern on induction and persistence of SCEs in peripheral lymphocytes and formation and persistence of the specific adduct N-3'-(2-hydroxyethyl)-histidine in hemoglobin, groups of male New Zealand white rabbits were exposed to ethylene oxide (ETO) at 200 ppm or 400 ppm for 6 h a day, 5 days a week or to 1500 ppm twice a day for 15 min until all groups reached an equal concentration-time (Ct) product of 4.8 X 10(4) ppm.h. Results show that both induced SCEs and the specific histidine adduct in hemoglobin reflect cumulative ETO exposure whether it occurs chronically at a concentration of 200 ppm or to brief exposures at the 7.5 times higher concentration of 1500 ppm. Haber's rule appears to be in effect over this range of exposure concentrations and times. Persistence of these effects appears not to be related to exposure concentration nor exposure pattern. These results contribute to further understanding of alkylating chemical mutagen dosimetry and of SCE and hemoglobin adducts as indices of exposure.