The effectiveness of epinephrine was compared to that of a combination of epinephrine and aminophylline in the initial treatment of acute asthma. Forty-four patients with 51 episodes of acute asthma were evaluated. Peak flow spirometry served as an objective measure of airway resistance, and theophylline levels were determined at fixed intervals throughout the study. Epinephrine and aminophylline were not found to be superior to epinephrine alone. There was no correlation between mean serum theophylline levels and the magnitude of improvement. Rapidity of emergency department discharge and frequency of admission was independent of treatment method. The failure of epinephrine-aminophylline to effect more rapid or profound improvement in pulmonary function might suggest that epinephrine alone, or an equivalent sympathomimetic is a rational choice in the initial treatment of acute asthma.