For the past two years we have treated patients with flail chest injuries and concomitant respiratory failure with intermittent mandatory ventilation (IMV) and positive end-expiratory pressure (PEEP). Prior to 1972 these patients were treated with controlled mechanical ventilation (CMV) until gross flailing ceased and inspiratory force and vital capacity measurements were adequate. We retrospectively studied the charts of 37 consecutive patients to compare the length of mechanical ventilatory support of patients managed by conventional CMV with those ventilated with IMV and PEEP. The mean ventilation time of patients treated with IMV and PEEP (5.1 +/- 4.7 days) was significantly less than that of the patients treated with CMV (18.8 +/- 14.4 days) (P less than .001).