The concentration of halothane and ethanol in operating rooms was measured during 37 routine operations performed in nine different departments of surgery at six different hospitals. The time-weighted halothane concentrations in the respiratory zones of anesthetic and surgical nurses were 0.3--34.0 ppm (time-weighted average 7.2 ppm) and 0.1--9.2 ppm (time-weighted average 2.5 ppm), respectively, in the different operating departments. The corresponding ethanol concentrations were 0.3--36.5 ppm (time-weighted average 12.5 ppm) for anesthetic nurses and 1.5--46.6 ppm (time-weighted average 15.3 ppm) for surgical nurses. The anesthetic technique influences the exposure of the operating staff to anesthetic gases, but it does not affect exposure to ethanol. In controlled experiments volunteers were exposed to low concentrations of halothane or ethanol. About 60% of both substances was retained. The content of ethanol in the end-expired air approached zero within a few minutes after the end of exposure, while low residual concentrations of halothane were demonstrable for more than 1 h. Although exposure to ethanol is insignificant in relation to the metabolic capacity of the body, ethanol indicates the presence of volatile disinfectant components, and its spread through the room atmosphere should be kept in mind when the ventilation of operating rooms is designed. The effective elimination of airborne pollutants in operating rooms calls for good general ventilation in conjunction with local exhaust close to the sources of anesthetic gas leakage. General ventilation mainly affects the concentration of substances well-mixed with the room atmosphere, such as volatile disinfectant components and anesthetic vapor that has spread beyond the actual work zones of the medical staff. For a significant reduction in the concentration of anesthetic gases in the respiratory zones of the medical staff, the gases must be vented at the source of leakage. Since airborne anesthetics occur not only in operating rooms, general ventilation has to meet certain minimum requirements also in anesthetic induction rooms and recovery rooms. Operating rooms and anesthetic induction rooms must also be supplied with local exhaust systems.