Pre-hospital self-administered analgesia using a 50:50 mixture of nitrous oxide and oxygen (Entonox) was evaluated in 240 patients. Of these, 93.4 per cent experienced either complete or partial relief from traumatic, chest, abdominal or back pain. Drowsiness was the most common side effect noted. No complications occurred during delivery of the mixture. Attention is drawn to the effect of extreme temperatures on the Entonox mixture and recommendations are made with respect to its use below-freezing climates. Because of its ease of use and short duration of action, Entonox appears to be well suited for the treatment of pre-hospital pain by Emergency Medical Technicians.