In the Department of Respiratory Medicine, North Staffordshire Hospital, patients fulfilling the Department of Health criteria for long-term oxygen therapy (LTOT) attend a practical teaching session on the use of their oxygen concentrator before commencing therapy. In the present study, we have audited the prescribing of LTOT in all patients in three health districts in the North West Midlands reviewed between June 1992 and July 1994. They were split into two groups. The first had the assessment and training programme in the department. Patients in the control group had been prescribed LTOT from outside the department without any formal training. In both groups of patients information was collated 6 months after starting LTOT by means of a questionnaire assessing patients', understanding of both their need for oxygen and their disease process, the dangers of oxygen therapy and present smoking habit. Objective information about the usage of each concentrator was obtained from engineer reports. Thirty-six patients (eight from the trained group and 28 controls) died before evaluation at 6 months. Forty-five patients (29 male, mean age 71 years) received training and 41 control patients (24 male, mean age 72 years) were evaluated. Thirty-seven (82%) patients who had received formal training were using their concentrator for greater than 15 h compared with only 18 (44%) of the controls (P = 0.0002). Forty-two (93%) patients who had received training understood why they were using LTOT compared with only 17 (41%) in the control group (P = 0.00001). Although both groups had a similar understanding of the dangers of smoking while on oxygen therapy, six (15%) of the control group were smoking as compared to only one (2%) of the trained group (P = 0.038). One of the control patients had received significant facial burns as a direct result of smoking while on oxygen. Further efforts are required to ensure that all patients prescribed LTOT should have a formal respiratory assessment as well as training to improve compliance and to obtain maximal benefits from such therapy.