Two types of benzodiazepines were used in premedication of flexible bronchoscopy. The agents were introduced in randomized, double-blind trial. Midazolam (Dormicum Hoffmann-La Roche AG) was given to 21 patients (0.07 mg/kg i.v.), diazepam (Seduxen Richter) to 22 patients (0.14 mg/kg i.v.) and placebo (saline) to 20 patients (0.07 ml/kg i.v.). Vigility, motor functions and anxiety were estimated from the application to 3 hours after endoscopy. Breathing, pulse rate, blood pressure and local reactions were followed as well. The course of bronchoscopy, anterograde amnesia and acceptability of further intervention were evaluated. Midazolam offered short term action, stronger sedative and anxiolytic effect than diazepam (48% to 27%). The anterograde amnesia was more frequent (90.5% to 55% in diazepam), acceptability of further bronchoscopy after midazolam was present in 95% of patients, after diazepam in 86% of patients. These favourable properties can be utilized especially in cases with enhanced anxiety and necessity of further endoscopies.