The authors describe the course of a severe asthma emergency in a boy aged 13 years. Respirator therapy and bronchial lavage were required. A therapeutically effective serum concentration was initially obtained by an aminophyllin infusion (dose 1.2 mg/kg b.w./h after bolus injection with 6 mg/kg b.w.). In the further course of treatment the theophyllin concentration in serum decreased considerably. The advantage of theophyllin determination for guaranteeing a safe therapy is explained on the base of this case report.