Various studies have implicated generalized health problems with chronic exposure to trace levels of nitrous oxide. Recent investigations have reported that higher-than-recommended levels of nitrous oxide exist in the breathing zone of the dental staff. This study was undertaken to accurately determine waste nitrous oxide levels during pediatric sedations and to evaluate the effect of scavenging in reducing environmental exposure. Conscious sedations were performed on 20 uncooperative 2-4-year old children. Each child was assigned randomly to one of two groups, a scavenged group and a nonscavenged control. Sedations were accomplished with oral administration of chloral hydrate and hydroxyzine. All patients received nitrous oxide (40%) in oxygen throughout the procedure. Waste nitrous oxide levels were monitored 22-24 in from the dentist's nose using an infrared spectrophotometer and recorded by a microprocessor. Results indicate that environmental levels of nitrous oxide exceed the National Institute for Occupational Safety and Health (NIOSH) recommendations by 12 times, regardless of whether a scavenging system was employed or not. It is concluded that the scavenging system tested in this investigation may not be as efficient as previously thought at complying with NIOSH recommendations.