Sixteen patients with asthma and/or chronic obstructive lung disease were treated for 8 days by scored tablets of sustained-release theophylline. Treatment was administered as a single evening dose per day, 2 hours after dinner, at a daily dosage of 10 mg/kg/day of theophylline. The theophylline curve remained in the theoretical therapeutic zone of 8 to 15 mcg/ml for about 14 hours; the clinical efficacy, evaluated on the basis of the improvement in the signs and symptoms, was satisfactory. The clinical acceptability was good apart from insomnia observed during the first 2 days of treatment.