A prolonged therapeutic effect following a single oral dose of theophylline and maintenance of an adequate therapeutic blood level of theophylline is an important factor in the management of chronic bronchial asthma. Eighteen adult asthmatics, nine of whom were females and nine males, aged between 21-53 years, were given a sustained release theophylline capsule, 250 mg, every 12 hours and pulmonary mechanical functions as well as serum theophylline levels were studied. All patients received Elixophyllin Elixir, 250 mg, and their serum level as well as pulmonary functions were studied and compared to those after receiving the sustained release capsules. In these patients, after isoproterenol inhalation, an average of 25.6% improvement in FEV1 was observed while after placebo there were very minimum changes. At the steady-state of sustained release theophylline capsule administration, an average of 20% improvement of FEV1 was observed at the five hour period and sufficient bronchodilation expressed as FEV1 was observed for a 10-12 hour period. Indeed, a sustained release theophylline capsule fulfilled the requirement that it adequately maintained therapeutic theophylline level of the blood and improved bronchodilation lasting up to 12 hours.