Postoperative blood losses after open-heart surgery for Tetralogy of Fallot made re-operation imperative in 15 out of 44 patients (34%, Series A). A surgical bleeding point proved to be the causative factor in only 2 cases; the others were believed to be caused by disturbances of the haemostatic mechanism, particularly by low platelet counts, apparently due to extracorporeal circulation. Administration of a platelet suspension after disconnection of the extracorporeal circuit diminished the number of bleeding complications significantly: in a series of 58 patients (Series B), 8 re-operations (14%) were necessary. In 3 of these cases, technical reasons could be found for the blood losses. Haemodilution was carried out routinely in both series. However, the diluent contained a pasteurised protein solution in Series A and fresh frozen plasma in Series B in order to minimize the deficit of coagulation factors as much as possible.