PATIENTS with an acute, diffuse pulmonary infiltrate pose substantial diagnostic and treatment challenges. Some such patients' conditions may qualify, when first examined, for a diagnosis of adult respiratory distress syndrome (ARDS). That syndrome consists of the presence of diffuse pulmonary infiltrates of unknown cause, arterial hypoxemia (due to a "right-to-left shunt" mechanism), and a normal pulmonary capillary ("wedge") pressure.1 Other patients with somewhat less severe involvement may seem to be approaching fulfillment of the criteria for a diagnosis of ARDS.
Part of the challenge posed by such patients is that some 30% have pulmonary infection as the basis for ARDS2; in the remainder, the pathogenetic basis is noninfectious and related to a biochemical-cellular sequence that has yet to be defined. Treatment of the latter is presently supportive; good support includes the avoidance of procedures that may further compromise respiratory function. It is also clear, however, that when infection