A 29-year-old woman with systemic lupus erythematosus (SLE) developed dyspnea, hemoptysis, pleuropericarditis, and azotemia shortly after an episode of arthritis and progressive hair loss. She had a high titer of radioimmune anti-DNA Antibodies, positive fluorescent anti-smooth muscle antibodies, and depressed C3 levels in her serum. Antiglomerular basement membrane antibodies were negative, and the titer of antibodies against extractable nuclear antigen was within normal limits. Cryoglobulins and lupus erythematosus cell preparations were negative. Despite steroid therapy and other supportive measures, including dialysis, she died ten days after admission. Percutaneous renal and pulmonary biopsies were performed postmortem at bedside and were processed for immunohistology. Identical granular deposits of C3 and IgG were found in both the lungs and the kidneys. This finding suggests that a common pathogenetic mechanism is operating in the development of pneumonitis and nephritis in SLE, and is in agreement with the currently held views on immune-complex diseases.