In addition to an innate functional dysmaturity of the neonate's immune system, operation, anaesthesia, and intensive care measures can significantly worsen this physiological immune deficiency. Given the fact that antimicrobial therapy as well as progress in intensive care of infected operated neonates and prematures did not significantly decrease the high mortality rate in this patient age group we began performing fresh-blood exchange transfusions as supportive immunotherapy in the treatment of neonatal septicaemia. Since indication for exchange transfusion has been adopted as early as septicaemia was suspected only 46% of the operated neonates (13 out of 28) died of their infection, compared to 82% of the patients (23 out of 28) who did not undergo exchange transfusion.