To the Editor: The use of positive end-expiratory pressure (PEEP) during ventilator therapy for acute exacerbation of symptoms in chronic obstructive lung diseases has received little attention. Small increments of PEEP (up to 6 to 8 cm H2O during mechanical ventilation) appear to decrease the excessively large functional residual capacity in patients with chronic airflow limitation and constitute a substitute for the patient's own pursed-lip breathing during spontaneous ventilation.Several years' experience with such patients has led us recently to try PEEP at high levels (intended to match the severity of bronchiolar spasm) in two moribund patients . . .