We report an effective method of scavenging nitric oxide and nitrogen dioxide. We have compared three agents, a commercially available filter, soda lime and activated charcoal, for their effectiveness and duration of action. Complete absorption of nitric oxide and nitrogen dioxide for a period of 170 h was obtained using the commercial filter. However, soda lime and charcoal were unable to successfully scavenge either gas. The resistance characteristics of this filter when dry or humidified were determined.