OBJECTIVE To quantify the exposure of operating room personnel to sevoflurane and nitrous oxide. METHODS Prospective study at a university hospital. METHODS In 25 patients undergoing elective surgical procedures, anaesthesia was induced with thiopentone/etomidate, vecuronium and fentanyl and maintained with fentanyl, sevoflurance in 35% oxygen and 65% nitrous oxide (N2O). Occupational exposure to sevoflurane and N2O was measured in the breathing zone of one representative of each of three personnel groups (anaesthetist, surgeon, auxiliary nurse) by means of a direct reading instrument using photoacoustic infrared spectrometry. RESULTS The mean trace concentrations of sevoflurane for the single anaesthetic procedures exceeded the 0.5 ppm level in more than 50% of the measurements. The 2 ppm level was not exceeded in the case of the anaesthetist and the surgeon, but was exceeded in 16% of the measurements for the auxiliary nurse. The level of 25 ppm N2O were exceeded in 28% of the measurements for the anaesthetist and in 16% of these for the surgeon and for the auxiliary nurse. CONCLUSIONS To keep exposure low, sevoflurane and N2O were used in a modern working environment: a low-leakage anaesthesia machine, high room ventilation rates, scavenging system, no intermittent mask ventilation, low to medium concentrations of sevoflurane, and strict control of the cuff pressure. Nevertheless, exposure could not be kept under NIOSH threshold values in all cases.