The level of N2O contamination in the breathing zone of anesthesiologists was measured while they administered inhalation anesthesia by mask to five patients. A mask gas-scavenging attachment was used for 30 minutes and then removed while anesthesia continued for a further 30 minutes. The levels of N2O with and without the scavenging attachment were compared. Using the scavenging attachment, N2O contamination was reduced from greater than 150 ppm to less than 5 ppm, a level well below the 25 ppm limit recommended by the National Institute for Occupational Safety and Health. The scavenging device is a simple and effective way to reduce operating room contamination with N2O during delivery of anesthesia by mask.