The effects of six different modes of therapy on arterial pH, pCO2pO2and pulmonary function tests were measured in 18 patients with asthma. No uniformly predictable outcome was observed with any of the treatment programs. Improved values were best sustained with epinephrine and aminophylline. All patients had hypoxia initially prior to therapy with arterial oxygen tensions ranging from 38 to 75 mm Hg. In some patients the arterial pO2worsened as a result of treatment with decreases ranging from 1 to 25 mm Hg. It is concluded that all patients with acute asthma should receive oxygen therapy initially and throughout their course of treatment with bronchodilators.