Transfusion-related acute lung injury (TRALI) is an infrequent but life-threatening complication of hemotherapy. The findings in 36 cases are described. The typical clinical presentation includes acute respiratory distress characterized by hypoxemia and fulminant pulmonary edema. The onset is usually within 4 hours of transfusion and is accompanied by hypotension. In most patients (81%), recovery is rapid and complete. In 89 percent of cases, granulocyte or lymphocytotoxic antibodies are found in the serum of the implicated blood product which contained plasma. HLA-specific antibodies were identified in donor serums in 65 percent of cases evaluated. The passive transfer of these antibodies may promote complement activation and subsequent pulmonary injury. TRALI is an important cause of transfusion-associated morbidity and is probably often misdiagnosed. Blood banks need to identify donors whose plasma causes these reactions in order to prevent their recurrence.