Oxygen therapy for use in the home can be prescribed in two forms: oxygen concentrators are used to provide long term domiciliary oxygen therapy (LTOT), and oxygen cylinders are used to provide oxygen intermittently for relief of symptoms. In this study prescription and usage of oxygen cylinders in the home were assessed. All patients using oxygen cylinders at home in the London Borough of Tower Hamlets in October 1992 were studied. A questionnaire was sent to each patient; further information was obtained from a questionnaire to the general practitioner and from hospital notes where available. Patients with a diagnosis of chronic obstructive pulmonary disease (COPD) were visited at home to measure oxygen saturation levels (SaO2). The main outcome measures were the proportion of oxygen cylinder users who had undergone a full respiratory assessment and the number who might benefit from LTOT. There were 56 patients using oxygen intermittently, 77% with COPD of which 28% had an SaO2 < or = 92%. In these 56 patients 27% had not been assessed by a hospital physician for their chest disease, 58% used their oxygen at least once a day and on average these patients used three cylinders each per month. Most patients using oxygen cylinders at home have a diagnosis of COPD and use oxygen regularly for short term relief of breathlessness; many have not been assessed by a respiratory physician. Measurement of SaO2 suggested that a significant minority might benefit from LTOT and would certainly warrant further evaluation.