The efficacy and safety of different regimens of intravenously administered enprofylline, an anti-asthma xanthine, were evaluated in a randomized open study, including 155 patients with acute exacerbation of obstructive lung disease. The regimen 2.5 mg/kg i.v. over 10 min was canceled after seven patients had been included, due to two cases of hypotensive/vasovagal reactions. The regimens 2.0 mg/kg/20 min and 2.5 mg/kg/20 min were significantly more effective with regard to bronchodilation than 2.0 mg/kg/10 min (PEF increase +35%, +30% and +17% respectively). Nausea and headache were the most common side effects (16-33% and 23-33% of the patients respectively on different regimens) with the lowest frequency on 2.0 mg/kg/20 min. Four additional hypotensive reactions occurred; one on each 2.0 mg/kg regimen and two on 2.5 mg/kg/20 min. The regimen 2.0 mg/kg20 min was found to be the most favourable with regard to efficacy and side effects. Enprofylline i.v. was found to be an effective bronchodilating treatment of acute airway obstruction but the frequency of side effects has to be considered.