The aim of this study was to evaluate the effects of propofol administration (2 mg.kg-1 i.v.) on the airways resistances and respiratory mechanics of patients affected by COPD exacerbation, requiring mechanical ventilation. Twenty patients required anaesthesia for diagnostic or therapeutic procedures. Fourteen consecutive patients were divided at random into two groups: Group P received propofol and Group C (control) received only Intralipid 10%; an additional group of six patients received i.v. flunitrazepam (0.03 mg.kg-1). Lung mechanics (dynamic and static compliance, peak inspiratory pressure, intrinsic positive and expiratory pressure, minimal and maximal resistances of the respiratory system) were evaluated in basal conditions and 3 and 6 min after propofol, Intralipid or flunitrazepam administration. We did not observe significant variations of the evaluated variables after Intralipid or flunitrazepam (Groups C and F), while in patients who received propofol (Group P), we observed the following modifications: dynamic compliance increased from 2.3 +/- 0.3 to 2.8 +/- 0.4 ml.kPa-1 (P < 0.05), peak inspiratory pressure decreased from 3.3 +/- 0.7 to 2.8 +/- 0.4 kPa (P < 0.05), minimal resistances of the respiratory system (that mainly reflect airways resistances) decreased from 1 +/- 0.2 to 0.7 +/- 0.2 kPa.l-1 x s-1 (P < 0.01). Our results suggest that propofol induces bronchodilation in mechanically ventilated COPD patients, and that this effect is not related specifically to the induction of general anesthesia.