An antirecurrence effect of theophylline was studied in 32 children aged 3 to 12 years suffering from severe bronchial asthma. The drug dosage was determined by means of a stepwise increase of a daily dose in the range of 10-30 mg/kg/day under control of the patient's general condition and parameters of external respiratory function. Blood theophylline concentration was measured by an immunofluorescent method. The drug individual biotransformation was revealed. Euphylline proved to be a highly effective and safe antirecurrence agent in an individual selection of doses and administration regimens. Combination of theophylline with inhalation beta-adrenomimetics and corticosteroids potentiates its clinical effect without influencing biotransformation.