The acute pulmonary and cardiovascular effects of single doses of theophylline 130 mg and terbutaline 2.5 mg administered alone and in combination were compared with placebo over a period of seven hours in 16 stable asthmatic subjects. Terbutaline 2.5 mg produced significant bronchodilatation that peaked at three hours and lasted for four to six hours. Theophylline 130 mg produced small increments in serum theophylline concentration (1.5-4.5 microgram/ml), did not produce greater bronchodilatation than placebo and did not provide additional bronchodilatation when combined with terbutaline 2.5 mg. The clinical implications of these findings with respect to the possible utility of combining low doses of theophylline with low doses of a beta-adrenergic stimulant are discussed.