The effects of 50% nitrous oxide and 50% oxygen and of 30% nitrous oxide and 70% oxygen were evaluated in 88 patients with significant pain while in the prehospital setting. Under the telemetry physicians' supervision, EMT-Ps directed patients in the technique of self-administration of the analgesic gas. Fifty percent (36/72) reported complete or almost complete amelioration of pain; all but 15% (11/72) reported some degree of relief. No patients experienced clinically deleterious side effects, although 48% (41/85) reported side effects, of which 90% were mild. The analgesic properties, lack of complications, quick onset and short duration of action, and acceptance by patients, physicians, and paramedics make N2O a nearly ideal analgesic agent for advanced life support use in the prehospital relief of significant pain.