The sudden development of diffuse pulmonary infiltration in a patient with SLE presents difficult diagnostic and therapeutic problems to the clinician. In the past ten years, we have seen eight patients with this problem. Neither roentgenograms nor clinical findings were specific. In six patients, pulmonary hemorrhage was found, but in only two of them did it exist alone. In the other four, heart failure, uremia, and coagulopathy complicated the findings. In one patient, P carinii was the cause; in one congestive heart failure, which was not obvious clinically or radiologically, was the cause. Three patients died: one of uncomplicated pulmonary hemorrhage, one with pulmonary hemorrhage occurring during the treatment of pneumonia due to L bozemanii, and one with pulmonary hemorrhage and multiple complications including sepsis due to Candida. On the basis of this experience, we have recommended a plan of action for physicians facing this problem.