As part of analyses carried out by the BGW, the working conditions in doctors’ practices with operating areas were investigated to establish whether the limit values for anaesthetic gases and disinfecting agents in air were being observed in the practices, and whether safe working conditions can be defined for staff. For this purpose, a total of 463 determinations were carried out in 15 different practices on different days and during various operations, with sampling in the area of the anaesthetist, the operating room personnel and at another fixed position in the room. In the working areas of the anaesthetists and other operating room personnel a total of 203 determinations of different materials were carried out. The limit value was observed in 98 percent of cases. In the case of the 216 stationary samples, the limit values were found to have been exceeded in 7 cases (4 %). In the assessment of the evaluation indices, which record the effect of all materials in the work area, limit values were exceeded for the anaesthetists in 4 cases (11 %) and for the operating room personnel in 3 cases (9 %). On closer examination, poor ventilation conditions were found to be present during the series of analyses concerned, with the flow of fresh air being less than 270 m3/h. This also applies for the evaluation indices of the stationary area. Here, limit values were exceeded in 8 cases with poor ventilation conditions. An important influencing factor in these investigations was determined to be the level of ventilation in the operating area. The exposure of personnel in all work areas decreased with increasing ventilation. With a fresh air flow of more than 270 m3/h the limit values were not exceeded. This investigation of doctors’ practices with operating areas allows the conclusion to be drawn that with the use of low-flow anaesthetic systems and the anaesthetic techniques documented in this report, the ventilation requirements stipulated in TRGS 525 („Technische Regeln für Gefahrstoffe“ – Technical Regulations for Hazardous Substances) are not necessary to observe the air limit values. From the point of view of the management of hazardous substances, a fresh air flow of at least 500 m3/h appears to be sufficient to guarantee observance of limit values in these practices during the normal handling and use of dangerous materials.