Daily general practice of theophylline dosing in chronic obstructive lung disease seems not strictly to follow therapeutic guidelines. To evaluate the efficacy of such an approach with regard to attaining therapeutic and safe plasma theophylline concentrations and clinical benefit, 103 patients with chronic obstructive lung disease were selected from the computerized database of a post-marketing survey. Dosing of theophylline was found to be independent of reference parameters, i.e. anthropometric data, age and clinical severity of the disease. Standard doses of 400 and/or 600 mg controlled-release theophylline, i.e. 7.9 mg/kg.day resulted in steady-state plasma concentrations of 10-20 micrograms/ml in 45.1% of patients and 5-10 micrograms/ml in 52.9% of cases. The increase in forced expiratory volume in 1 s at steady-state, evaluated by the percentage frequency distribution of changes from baseline was significant in all patients. In conclusion, not withstanding the daily therapeutic practice of controlled-release theophylline dosing and, at times, lower than optimal plasma levels, clinical and functional recovery was obtained in a large percentage of cases.