Several drugs have been employed for sedation during flexible fiberoptic bronchoscopy (FOB). Clonidine attenuates stress-induced sympathoadrenal responses and has sedative properties. We investigate the effects of clonidine premedication on hemodynamic and comfort parameters of patients submitted to FOB under airway topical anesthesia only. Patients received placebo (n = 22; men = 16; median age = 50.5 years) or intravenous clonidine (3 microg/kg; n = 20; men = 15; median age = 46.0 years) 15 min before FOB. Blood pressure (BP), heart rate (HR), plasma norepinephrine (nor) and cortisol levels were measured before, during, and 1 h after FOB. Comfort was assessed by the examiner and by the patients using a visual numerical scale (0-10). The placebo group showed significant increases in systolic BP, HR, and nor levels during FOB (SBP = 125 mmHg x 145 mmHg; HR = 74 bpm x 85 bpm; nor = 316.2 pg/dl x 483.1 pg/dl), whereas clonidine group did not display such changes. Clonidine group showed a lower frequency of cardiac arrhythmias than the placebo group during and after FOB (supraventricular = 39% x 50%; ventricular = 22% x 40%). Levels of comfort were high and comparable in both groups. We concluded that although clonidine led to a somewhat better hemodynamic profile, it did not contribute to better comfort in this setting.