The aim of this randomised study was to compare the effects of iron lung ventilation (ILV) with invasive mechanical ventilation (IMV) in patients with acute respiratory failure (ARF) due to exacerbation of chronic obstructive pulmonary disease.Forty-four patients with ARF were assigned either to ILV (22 patients) or IMV (22 patients). Primary end-points were the improvement in gas exchange and complications related to mechanical ventilation.On admission ILV and IMV groups did not differ in age, simplified acute physiology score II, arterial oxygen tension (Pa,O 2 )/inspiratory oxygen fraction (FI,O 2 ), arterial carbon dioxide tension (Pa,CO 2 ) and pH. Compared with baseline, ILV and IMV induced a similar and significant improvement in Pa,O 2 /FI,O 2 , Pa,CO 2 and pH after 1 h of treatment and at discontinuation of mechanical ventilation. Major complications tended to be more frequent in patients treated with IMV than in those treated with ILV (27.3% versus 4.5%), whereas mortality rate was similar (27.3% versus 18.2%). The ventilatorfree days and the length of hospital stay were significantly lower in the ILV than in the IMV group.This study suggests that iron lung ventilation is as effective as invasive mechanical ventilation in improving gas exchange in chronic obstructive pulmonary disease patients with acute respiratory failure, and is associated with a tendency towards a lower rate of major complications. Endotracheal intubation and mechanical ventilation in patients with chronic obstructive pulmonary disease (COPD) and acute or chronic respiratory failure are associated with several complications [1,2]. Compared with standard medical therapy, noninvasive positive pressure ventilation (NIPPV) reduces the need for endotracheal intubation [3][4][5], the length of hospital stay [3], and the in-hospital mortality rate [3][4][5][6]. Recently, it was shown that in COPD patients with severe respiratory failure that failed medical therapy in the ward, NIPPV compared with invasive mechanical ventilation (IMV) resulted in a similar mortality rate, length of hospital stay and duration of mechanical ventilation [7].It has been reported that COPD patients with severe respiratory acidosis and hypercapnic coma can be successfully treated with iron lung ventilation (ILV) [8]. A case-control study [9] suggested that ILV is as effective as IMV in the treatment of COPD patients with acute on chronic respiratory failure and is associated to a shorter duration of ventilation, and a similar length of hospital stay. Nevertheless, to date, no randomised study comparing ILV with IMV for the treatment of exacerbation of COPD has been carried out.The aim of this prospective controlled, randomised, pilot study was to compare the effects of ILV and IMV on gas exchange and the rate of complications associated with mechanical ventilation in COPD patients with acute on chronic respiratory failure.