The use of nitrous-oxide (10024972) as an inhalation anesthetic in dentistry has been recently suggested to be hazardous to the health of dental personnel. Control measures developed for achieving maximum reduction of concentration of anesthetic inhaled by the dentist without modification of safe anesthetic practices include the use of special scavenging mask, venting of the patient suction machine, preventive maintenance for anesthetic equipment, leak testing of the equipment, air sweep fans to dilute the concentration of anesthetic inhaled by personnel, monitoring nitrous-oxide in the breathing zone of the dentist. Without the above control measures, the concentration of nitrous-oxide measured in the dentists' breathing zone averaged 900ppm. Use of the above measures was effective in reducing the dentists' inhaled mean concentration to 14ppm, representing a negative 98 percent reduction. These data were obtained during the conduct of 157 dental procedures completed in the operatories of four general dentists, two oral surgeons and two pedodontists. In an additional series of 47 anesthetic procedures studied in an oral surgical suite with two companion operatories where control measures were applied, the dentists' mean inhaled concentration of nitrous-oxide was 31ppm. On the basis of these studies, a concentration as high as approximately 50ppm nitrous-oxide measured under the specified circumstances is presented as reasonably achievable during routine dental anesthesia or analgesia.