In the present study we evaluated the occupational exposure to N2O and isoflurane during open circuit (OC) (fresh gas flow > or = minute volume) and low flow (LF) (fresh gas flow = 1.5 l/min) anaesthesia. The effects of active scavenging and of a charcoal filter positioned on the exhausting branch of the ventilator on environmental and urinary concentrations of inhalation anaesthetics were also investigated. The study was carried out in the same operating room provided with non-recirculating air changes (10 per hour). It involved anaesthetists and nurses during routine activity. N2O and isoflurane concentrations (time-weighted average) were measured after 3-hour continuous exposure: 1) in the environment at the level of the personnel's breathing zone (Ci); 2) in the environment at the ventilator zone (C); 3) in urine (Cu). During OC anaesthesia without active scavenging the breathing zone concentration of both N2O and isoflurane was very high (194.6 +/- 15.2 and 5.0 +/- 0.4 ppm, respectively). The activation of the scavenging greatly reduced the breathing zone concentration of N2O (31.6 +/- 4.1 ppm) and isoflurane (1.7 +/- 0.2 ppm). LF anaesthesia (with active scavenging) significantly reduced the environmental concentration of both anaesthetics (Ci N2O and isoflurane 22.7 +/- 1.8 and 0.6 +/- 0.04 ppm, respectively). During LF anaesthesia the breathing zone concentration of N2O remained low, even without scavenging (22.7 +/- 1.8 ppm). Similar results were obtained by measuring N2O and isoflurane concentrations at the ventilator zone and in urine.(ABSTRACT TRUNCATED AT 250 WORDS)