The plasma concentration of lidocaine and its metabolite, mono-ethyl-glycine-xylidine, was measured furing fiberoptic bronchoscopy (FB) using an ultrasonic nebulizer to achieve topical anaesthesia. Most patients received additional anaesthesia of the laryngeal region and the tracheobronchial tree during the procedure. The achieved plasma concentrations showed that a substantial amount of lidocaine was absorbed, but toxic plasma levels were not reached. Lidocaine plasma concentration above the therapeutic range for treating cardiac diseases was observed in one patient. The use of an ultrasonic nebulizer with lidocaine before FB seems to give sufficient local anaesthesia and to be a safe method.