In a 64-year-old ventilated patient with severe chronic obstructive pulmonary disease and extensive unilateral pneumonia, intrinsic PEEP became recognized when the chest roentgenogram showed unilateral lung hyperinflation and herniation of a large bulla to the contralateral hemithorax. The use of an on-line suction catheter may have contributed to the development of intrinsic PEEP. Removal of the catheter resulted in roentgenographic and clinical improvement.