Twenty pediatric patients, age range 7-13 years, affected by asthma, have been treated with a sustained release preparation of theophylline once daily (mean dosage 13 mg/kg). The findings of plasma levels of theophylline below therapeutic range twenty four hours after dosing, in steady-state conditions, underline the need of individualized therapy specially in pediatric patients. The Authors observed a good therapeutic effect of this sustained release preparation, as expressed by improvement of symptomatology and pulmonary function tests, together with the sparing effect on other drugs. No side effects have been observed.