To the Editor .—The respiratory distress syndrome, as manifested by increased pulmonary venous admixture, continues to be an important challenge in the management of multiply transfused patients. The study presented in theArchives(113:947-950, 1978), addresses the efficacy of Swank micropore transfusion filters in preventing increased pulmonary arterial venous shunting in surgical patients. They present a considerable increase in shunting as well as alveolar-arterial oxygen difference in patients transfused over 20% of blood volume through standard transfusion filters, but no difference in the same parameters in patients who were transfused through Dacron wool filters. In evaluating their preoperative data, it is apparent that the groups were noticeably different before surgery and that both groups had identical shunts and alveolar-arterial oxygen differences postoperatively. In addition, if the single patient with substantially elevated preoperative shunting were excluded from consideration, postoperative shunting would actually be less in patients with standard transfusion filters. Although