In a single-blind, crossover study 10 adult asthmatic patients received a theophylline-ephedrine combination tablet (theophylline 90 mg, ephedrine 16 mg and phenobarbital 25 mg in an immediate release layer and theophylline 90 mg and ephedrine 32 mg in a sustained release layer) twice daily or terbutaline 5 mg three times daily for two weeks. There was no significant difference in bronchodilator response to a single dose of the study drugs on either the initial day of treatment or after two weeks of continuous therapy. Mean increases in serum cyclic-AMP levels produced by both drugs were not significantly different. Mean peak plasma theophylline levels were 2.9 +/- 1.3 microgram/ml following the initial dose and 7.3 +/- 3.4 microgram/ml after two weeks of continuous dosing with the combination drug. No adverse effects on blood pressure or pulse rate were observed to either drug. Overall, the incidence and severity of reported side effects (tremor, nausea and nervousness) were less with the theophylline-ephedrine combination.