To obtain data on oxygen use among hospital inpatients criteria for instituting, monitoring, and stopping oxygen therapy were formulated. The records of 90 consecutive patients who had been started on oxygen therapy outside the critical care areas of a university hospital were then examined. By the criteria, 79% of patients were deemed to have required oxygen therapy, 14.5% had been adequately monitored, and only 12% had had therapy terminated on the basis of appropriate physiological measurements. Prospective studies are required to validate monitoring recommendations and establish their cost-benefit ratio in terms of patient comfort and health-care costs.