BACKGROUND: The aim of this study was to evaluate the influence of oral clonidine premedication on respiratory mechanics by tracheal intubation in smokers. METHODS: Thirty male smoker patients were randomly divided into 3 groups. For group 1 (n = 10), l microgram/kg of clonidine was premedicated. For group 2 (n = 10), 2 microgram/kg of clonidine was premedicated. Group 3 (n = 10, control group) was the no premedication group. After anesthetic induction, CMV was applied with a Siemens Servo 900C ventilator, and anesthetic gases were supplied via the low pressure inlet of the ventilator. Tidal volume (10 ml/kg) was fixed during measurements for each patient. End-inspiratory occlusion was applied for at least 3 seconds and tracheal pressure was measured at the distal end of the endotracheal tube. Pressure, flow and volume were monitored and recorded with a Bicore CP-100 pulmonary monitor. Data were measured after 2 (100% O2) and 5 (1.5 vol% enflurane with 50% N2O) minutes of tracheal intubation. Data were transferred to PC and analyzed by processing software (ANADAT). Total respiratory (Rrs), airway (Raw) and tissue (Rve) resistances, along with static (Cstat), dynamic (Cdyn) compliances were calculated. RESULTS: There were no significant differences for Rrs, Raw, Rve, Cstat and Cdyn in the three groups. CONCLUSIONS: Oral clonidine premedication in dosages up to 2 microgram/kg do not affect the changes of respiratory mechanics caused by tracheal intubation in smokers.