In patients with acute exacerbations of asthma, the intravenous administration of bronchodilators, such as salbutamol, entails the potential risk of worsening pulmonary gas exchange, despite an amelioration of airflow obstruction. The present study was designed to investigate the effect of intravenous aminophylline on pulmonary gas exchange in patients hospitalized with a severe exacerbation of asthma. We studied 12 patients (aged 41 +/- 13 yrs) admitted to the hospital because of an exacerbation of asthma. The study was of a randomized, double-blind, placebo-controlled design. Six patients were treated with intravenous aminophylline and six received placebo, in addition to standard treatment with inhaled salbutamol and intravenous corticosteroids. Forced spirometry, respiratory gas exchange, ventilation-perfusion relationships assessed with the multiple inert gas elimination technique, and systemic haemodynamics were measured at baseline and 60 min after treatment started. In the aminophylline-treated group, mean theophylline plasma levels increased to 15.2 +/- 3.6 micrograms.ml-1, forced expiratory volume (FEV1) increased by 17 +/- 12%, and forced vital capacity (FVC) by 16 +/- 10%. The mean changes in FEV1 and FVC in the aminophylline-treated group were significantly higher than in the placebo-treated group. Likewise, minute ventilation increased by 23 +/- 14% and arterial carbon dioxide tension (PaCO2) decreased by 0.4 +/- 0.3 kPa (3 +/- 2 mmHg) during aminophylline infusion. No significant changes in arterial oxygen tension (PaO2) or in ventilation-perfusion distributions were shown in aminophylline-treated patients.(ABSTRACT TRUNCATED AT 250 WORDS)