Treatment of patients with severe acute respiratory insufficiency included application of end-expiratory pressure to an optimal level, precise cardiovascular monitoring, and adaptation of conventional respirators to provide intermittent mandatory ventilation. Of 90 patients with acute respiratory insufficiency secondary to trauma, sepsis, or complicated surgery, 65% survived. Mortality appeared to be independent of the level of end-expiratory pressure required. The goal of therapy was maximal reduction of intrapulmonary shunt without significantly decreasing cardiac function. In the group requiring more than 20 cm H2O end-expiratory pressure, shunt decreased from 48% at 5 cm of positive end-expiratory pressure to 21% at the optimal level. In only 6% of the entire group was significant pulmonary dysfunction present at the time of death. Most deaths (75%) were deemed secondary to failure of multiple organ systems, occurring late in the hospital course. Pneumothorax was recorded in 10% of the entire group. Acute respiratory insufficiency should be rapidly reversible in most cases if aggressive measures are employed with the intent of reversing functional impairment rather than improving arterial oxygenation to "satisfactory levels."