We report the findings on the exposure of veterinary hospital staff to isoflurane during the induction, maintenance and recovery from anaesthesia before and after implementation of corrective measures. The concentration of isoflurane was measured by highly sensitive, photo-acoustic infrared spectrometry over a 5-year period. Samples were taken from the breathing zones of the anaesthetist. The threshold in Austria for the time weighted average (TLV-TWA) concentration over 8 hours (80 mg/m(3) or 10 ppm) was not exceeded in any measurement; the short-term exposure limit (TLV-STEL) over 15 minutes (160 mg/m(3) or 20 ppm) was exceeded several times during mask induction, mask anaesthesia maintenance, patient disconnection from anaesthetic machines, equine surgery and equine recovery period and during the vaporiser filling time. Based on these findings, we made general recommendations to reduce the individual exposure to a level that is reasonably achievable. The rates of air exchange rates did not satisfy the recommended values and lay distinctly below the limit of 15 h(-1) for mechanically ventilated rooms in which inhalation anaesthesia is administered. The effects of the corrective measures were documented in the second part of the study.