The presence of toxins in the blood of burned or otherwise injured patients was indicated by the demonstration of cytotoxic effects on HeLa cells, cytolytic effects on red cells of other burned or injured patients, and precipitogens against serums from patients with healed burns. Such serums were shown to contain anti-toxic-antibody-like substances by demonstrating their ability to neutralize the cytotoxic effect on HeLa cells and by demonstrating the presence of hemolysins and precipitins. In preliminary clinical trials the transfusion of blood or plasma from donors with healed burns to critically toxic burned or injured patients was followed by prompt improvement. Serums obtained from the recipients after such transfusions were no longer toxic to tissue cultures. The authors recommend further clinical trials of antisera of known titer from persons with healed burns.