As a basis for risk estimations for ethylene oxide (EtO) exposure and for the establishment of occupational exposure limits in work environments it is important to know the ratio between the in vivo dose and the exposure dose of this compound. For an assessment of this ratio, data on hemoglobin adduct levels in occupationally exposed workers and exposure levels in the work environment have been collected. The in vivo dose is directly proportional to the product of the uptake and retention time (1/lambda) of EtO in the body. The rate of clearance (lambda) of EtO has been calculated for individual workers from adduct levels and estimated EtO uptake. The wide range of lambda values found (approximately 1-65 h-1) can only partly be ascribed to a true variation between individuals with respect to clearance rates. One uncertainty results from the difficulties to estimate EtO uptake. A better estimate of lambda (approximately 3 h-1) is probably derived from the measurements of environmental and instantaneous blood concentrations of EtO in exposed workers by Brugnone et al [Int Arch Occup Environ Health 58 (1986) 105-112].