A new oral bronchodilator, carbuterol, was studied in 9 subjects who had reversible airway obstruction. In addition to the spirometric changes, serial arterial blood gas determinations were done to see if the drug induced hypoxemia. Two- and 4-mg doses were compared with the placebo. There was a significant bronchodilating effect with the 4-mg dose beginning 30 min after administration of the drug. Maximal improvement of forced expiratory volume in 1 sec was observed at 4 hours, with a 42 per cent increase from the baseline. No significant hypoxemia was observed. The drug was considered an effective bronchodilating agent, with the effect lasting longer than 4 hours.