The benefit of continuous domiciliary oxygen therapy (OCD) directly depends on the number of hours the oxygen is used daily. The observance of a correct regime is rarely met at present. For this reason we have done a prospective study for 24 months, assessing the compliance of 64 patients from 28 to 82 years of age. All these patients received a systematic and personal programme of education for 2 days in hospital. We subsequently measured, without the knowledge, either of the patient or the person caring from them, the quarterly oxygen usage. The mean duration of oxygen therapy was 14.7 +/- 3.6 hours. It remained stable during the 2 years of observation: 51% of the patients achieved a treatment of 15 hours or more and 10%, 10 hours or less. We did not find a significant correlation between the hours of compliance and the age, sex, FEV1, FVC and PaO2 or haemoglobin saturation. A significant statistical correlation with the PaCO2 was obtained. The more educated patients had better compliance levels than those of lesser education. The results obtained were better than those found in the literature at the present time. Perhaps it is explained by the level of education given. It cannot be excluded, however, that our severe criteria for the prescription of OCD has selected a population which was more susceptible to achieving good compliance. However, these results encourage the initiation of another prospective study using a control group to make a better assessment of the impact of education on the patient and his carers by the improved compliance in OCD.