In 3 comparing series the behavior of platelets after experimental lung transplantation was examined in 33 dogs. After allogenic transplantations (21 animals) the ultrastructural findings were pathologic changes of the platelets, such as hyperaggregability with irreversible aggregation prevailing, as well as capillary wall alterations. X-rays showed considerable reduction of functioning parenchyma. Since these findings were absent in animals which underwent merely pulmonary re-implantation (4 animals) and can be considered a controll group, the authors conclude that these alterations are caused by mainly immunologic reactions. Acetylsalicylic acid given to animals with grafted lungs significantly inhibited is specific and certainly immuneinduced pathologic development. Absolutely necessary, therefore, appears the application of such aggregation inhibitor as additional treatment in lung transplantations.