We evaluated an oral theophylline loading-dose procedure that was designed to rapidly achieve and sustain theophylline serum concentrations of approximately 10 to 12 micrograms/mL. Ten healthy adults were given an oral loading dose of approximately 6 mg/kg of aminophylline, (Aminophyllin) (ie, 4.8 mg/kg of theophylline). Two hours later, each subject was given approximately 6 mg/kg of a sustained-release theophylline tablet (Theo-Dur). Serum samples were collected at 1/2, 1, 2, 3, 6, 9, and 12 hours, then assayed for theophylline concentration. The mean theophylline concentration (+/- SD) one hour after the initial loading dose was 10.5 +/- 2.3 micrograms/mL. Subsequent theophylline concentrations demonstrated minimal fluctuation, with means ranging from 10.7 +/- 1.6 to 13.6 +/- 2.8 micrograms/mL. Four of the subjects reported headache; none vomited or experienced severe nausea. We conclude that this method of oral theophylline loading can be effective in achieving prompt and sustained therapeutic theophylline levels without significant side effects and that this may provide a valuable therapeutic alternative in those asthmatic patients who do not clearly require intravenous aminophylline therapy.