The main contents of the forthcoming NIOSH criteria document on trace anesthetic gases are highlighted. Based on the available health data, NIOSH has concluded that a safe level of exposure to waste anesthetic gases cannot be defined and it has recommended that exposure to the halogenated anesthetics, when used alone, be controlled to the lowest concentrations that can be reliably and reproducibly quantitated using sampling and analysis methods recommended for field use. This concentration is 2 ppm, collected by charcoal adsorption from a 45 liter air sample over a period not to exceed 1 hour, followed by gas chromatographic analysis. When the halogenated anesthetics are used in combination with nitrous- oxide (10024972), it is recommended that exposures be controlled to the lowest concentrations feasible with available control technology. The method recommended for monitoring nitrous-oxide levels is infrared absorption analysis in combination with several sampling methods. The means used to conduct waste gases to the outside range from venting into a nonrecirculating air conditioning exhaust grille to installation of a special duct system or suction line.