Continuous sustained-release theophylline therapy was used in 61 children with severe asthma, aged 5 to 16 years. Mean treatment duration was 5 months 8 days (range: 8 days-16 months). The necessary dosage to obtain correct blood theophylline levels was 18 +/- 3.6 mg/kg/day (range: 10-31 mg/kg/day). The adaptation of the doses to blood theophylline levels and regular check-ups confirmed intrapatient variability and the dose-dependent disposition of theophylline. In 35 of the 42 children (82%) who were observed for more than 3 months, theophylline induced a decrease of the frequency of the attacks and a better attendance to school. Nine times out of 30, oral steroid administration or sustained-release cosyntropin injections could be stopped and in 15, the dosages could be decreased by at least 50%. Evaluations of pulmonary function, performed several times in 12 children, showed that theophylline induces significant bronchodilatation, mostly of the large bronchi.