Aim: Biomonitoring should clarify whether using medical devices sterilised by the gas ethylene oxide (EO) results in internal exposure due to residual EO. Analyses should assess effects of cumulative exposure over a period of several weeks. Methods: 30 employees (25 female, 5 male) of Augsburg Hospital were examined. 21 had been in contact with medical devices sterilised by EO. 12 workers unpacked these products within the stockroom or OP theatre (collective B1). Nine applied the products in OP theatre and wore EO sterilised coats (collective B2). The control group (K) consisted of nine employees in administration offices. EO reacts with haemoglobin in human erythrocytes yielding an adduct which can be analysed as N-(2-hydroxyethyl)valine (HEV). HEV and N-(2-cyanoethyl)valine (CEV) were analysed in EDTA-blood samples of the subjects, the latter in order to identify persons exposed to tobacco smoke which is an important confounder. Results: HEV results of four employees were not included within further evaluation because of tobacco smoke exposure (CEV above 0.1 μg/l). Each collective (B1, B2, K) contained three persons with HEV < 0.5 μg/l (limit of detection). The other 17 persons had concentrations of HEV ranging up to 1.3 μg/l blood. All values were smaller than the reference value (1.5 μg/l) derived from the German general population without occupational exposure. There was no difference between the collectives concerning HEV. The median values were calculated in B1, B2, and K as 0.5, 0.6 and 0.5 μg/l, respectively. Conclusion: An additional uptake of EO was not found under the existing working conditions.