The effect of the combination fenoterol-ipratropium bromide (Duovent) as a bronchodilator drug versus salbutamol and placebo was investigated in 20 patients with chronic obstructive lung disease in a random cross-over trial. Our study was performed not only to evaluate the bronchodilator response, but especially to quantify the possibly more prolonged action of Duovent versus salbutamol, based on registration of prevention of asthma attacks, time effects and protective activity, management and tolerance. Each patient received therapy for 3 weeks; in each week only one of the preparations: salbutamol, Duovent or placebo was used. Respiratory function tests were determined every week on the 3rd, 5th and 7th days at the same time exactly at 30 and 60 min after drug inhalation. Additionally we registered, for each patient, daily symptomatology (e.g., asthma attacks, cough, additional daily puff use, adverse reactions) by using a personal clinical diary. The results and analysis of the pulmonary tests (especially FEV1 and peak expiratory flow) confirmed the bronchodilator effect of both drugs, higher for Duovent but not sufficient to reach statistical significance. Clinical condition, regarding number, severity of asthma crises and additional puff use, showed a significant statistical variation for each symptom either as regards advantage of Duovent and salbutamol versus placebo, or advantage of Duovent versus salbutamol. Therefore, the results of this trial reveal an excellent bronchodilator effect of both drugs and confirm a higher clinical efficacy of Duovent if used in long-term treatment, with good tolerability.