The aim of this study was to determine if a relationship existed between some inhalation anesthetics airborne exposure levels (Cl) and the concentration of anesthetics in samples of urine produced throughout the exposure time (Cu. The concentrations of nitrous oxide (N2O), halothane (fluothane), enflurane (ethrane), and isoflurane (forane) in the ambient atmosphere were determined in 190 operating theaters of 41 hospitals in Italy. Nitrous oxide, halothane, enflurane and isoflurane were detected in the urine of 1521 exposed subjects (anesthetists, surgeons, and nurses). The environmental measurements were performed using personal passive samplers, and the biological measurements were performed using the head space method. Significant correlations were found between the anesthetics concentration in urine produced during the shift collected after a 4‐h exposure (Cu, μg/L) and anesthetics environmental concentration (C1, ppm). The results show that the urinary anesthetic concentration can be used as an appropriate biological exposure index. The biological values (urinary concentration values) proposed are the following: nitrous oxide, 25 μg/L, for an environmental value of 50 ppm; halothane, 97 μg/L, corresponding to 50 ppm of environmental exposure; 6.2 μg/L, corresponding to 2 ppm of environmental exposure; enflurane, 145 μg/L for an environmental exposure of 75 ppm and 5.6 μg/L for an environmental exposure of 2 ppm; isoflurane, 5.3 μg/L for an environmental exposure of 2 ppm. The values proposed are the respectively 95% lower confidence limit and therefore should be considered as a protection for the individual, especially if each biological value is corrected according to analytical variability of the measurements. In our opinion, the method of choice in the assessment of occupational exposure to inhalation anesthetics is the measurement of the urinary anesthetic concentration.