In 17 patients with moderate to severe asthma, we compared acute bronchodilator effects of the following drugs or drug combinations using a double-blind crossover design: terbutaline, 5; aminophyline 400; terbutaline, 5, plus aminophyline, 400; terbutaline, 2.5; aminophylline, 200; terbutaline, 2.5, plus aminophyline, 200 mg; and placebo. The higher doses of terbutaline and aminophylline alone produced comparable bronchodilation and similarly frequent adverse side effects; low doses of each drug also had comparable effects. The high-dose combination produced significantly (P less than 0.05) greater bronchodilatation than either drug alone. The low dose combination had bronchodilator effects comparable to those produced by the higher dose of either drug alone. These findings suggest therapeutic advantages in combining high doses of theophylline and an oral beta adrenergic agonist (terbutaline) in asthma not well controlled on high doses of either drug alone and in combining these drugs in lower doses in patients experiencing intolerable side effects from a high dose of either drug.