The aim of the study was to evaluate the efficacy of cough-preventing treatment with levodropropizine, a drug inhibiting peripheral cough reflexes, in patients undergoing bronchial endoscopy. Sixteen patients, aged 37-73 years, suffering from chronic obstructive lung disease in the hypersecretory phase, were included in the study. The experiment was designed as double blind with double observer, controlled versus placebo. As comparative efficacy parameters were considered the number of anaesthetic boluses (lidocaine at 2%) administered during and immediately after the manoeuvre. The number of coughs during and 10 min after bronchoscopy was registered on a magnetic tape and read by a blinded observer thereafter. Levodropropizine was given as oral drops (20 each time, equal to 60 mg active drug) 12 h and 1 h before bronchoscopy. Data analysis was performed by descriptive statistical tests and by the non-parametric Wilcoxon test for paired samples. Levodropropizine treatment significantly reduced the number of anaesthetic enemas (p less than 0.01), and presented an excellent tolerability and safety profile.