The objective of this study was to determine whether airway occlusion pressure (P0.1) is a useful predictor for successful weaning during discontinuation of assisted ventilation (AV) in patients with chronic obstructive pulmonary disease (COPD). We studied 12 patients with COPD receiving AV with maximal inspiratory pressure (MIP) less than or equal to -20 cm H2O and FVC greater than or equal to 10 ml/kg. The P0.1, VT, frequency, mean inspiratory flow rate (VT/TI), inspiratory time to total breath cycle duration (TI/Ttot), and arterial blood gases were determined just prior to weaning, within 5 min after discontinuing AV (Time 0), and at 30, 60, 90, 120, 180, and 240 min. Five of the 12 patients failed to wean, defined as requiring AV within 24 h after discontinuing AV. At Time 0, all patients who subsequently failed to wean had a P0.1 of greater than 6 cm H2O, and those who were successfully weaned had a P0.1 of less than 6 cm H2O (p less than 0.001), although the arterial blood gas determinations were comparable in both groups. Throughout the study period, P0.1 in the patients who failed to wean was persistently higher than in the successfully weaned patients. Despite the high P0.1, VT and VT/TI decreased significantly at the termination of the study compared with those at Time 0 in 3 of the patients who failed to wean. Tachypnea was not useful in predicting failure to wean. The TI/Ttot in the patients who failed to wean was persistently lower than in the successfully weaned patients. We conclude that P0.1 is an important indicator for successful weaning.