1. In the blood of some people with leukemia and other disseminated neoplastic diseases it is possible to demonstrate an abnormal hemolytic mechanism by incubating sterile blood in vitro at 37 C. for 24 hours. There is a latent period of 6 to 8 hours before hemolysis begins. Hemolysis can be inhibited by an excess of glucose or by low pH and also by removal of calcium. The heat stability of the system indicates that the plasmal abnormality is not enzymatic.
2. It is suggested that hemolysis is due to a reaction between ionic calcium and some component of the erythrocyte. The nature of the plasma abnormality that permits the reaction is not known.
3. The significance of this phenomenon in the pathogenesis of anemia in neoplastic disease has not been established.