An analgesic mixture of nitrous oxide and oxygen (Entonox) has been used in nine ambulances in Gloucestershire for self-administration by patients in severe pain. Over a period of three and a half months 66 patients have been treated. In all cases the pain was wholly or partially relieved, and in no instance was the patient's condition worsened. No undesirable side-effects attributable to Entonox were produced. It is recommended that other ambulance authorities should consider the use of Entonox in this context.