The results of NIOSH surveys of nitrous-oxide (10024972) exposures during cryosurgical procedures were presented. Environmental surveys were conducted at two facilities that used nitrous-oxide as the cryogenic gas in their surgical instruments. These instruments consisted of one or two 20 pound D-type cylinders connected to cryogenic probes by way of appropriate tubing and fitting. Neither instrument was vented. Nitrous-oxide exposures were measured during simulated and actual cryosurgical procedures using a portable infrared analyzer. The simulations were based on observed or reported work practices. Nitrous-oxide concentrations during a simulated procedure at the first facility (facility-A) that used a 4 minute freeze, followed by an 8 minute thaw and another 3 minute freeze peaked at 17,000 parts per million (ppm). This was equivalent to a 25 minute time weighted average (TWA) exposure of 7500ppm and was well above the NIOSH recommended standard of 25ppm. Assuming that no other nitrous-oxide exposures occurred, this exposure was equivalent to an 8 hour TWA exposure of 390ppm. At the second facility, a simulated procedure using a 3 minute freeze produced a peak nitrous-oxide exposure of 13,000ppm. This was equivalent to a 15 minute TWA exposure of 4000ppm and an 8 hour TWA exposure of 130ppm. Nitrous-oxide migrated into adjacent areas at both facilities. During two actual procedures at facility-A, nitrous-oxide concentrations of 195 and 140ppm were measured at a nurses station a short distance away. Measurements taken in an examination room after an actual procedure was performed at facility- A indicated nitrous-oxide concentrations still above 25ppm 70 minutes later. The author concludes that extremely high short term exposures to nitrous-oxide can occur during cryosurgery procedures. These exposures can be reduced by using local exhaust ventilation.