1. Dogs injected intravenously with dog erythrocytes containing one or more antigenic factors lacking in their own red cells developed iso-hemagglutinins and hemolysins exhibiting characteristics of immune antibodies.

2. Transfusions of incompatible whole dog blood and plasma were carried out under controlled conditions. Pretransfusion observations were made and followed by closely spaced post-transfusion measurements of serologic and hematologic alterations.

3. The rate of destruction of incompatible donated corpuscles was determined by tagging the cells with radioactive iron and also by employing the technique of differential agglutination of erythrocytes. It was thereby shown that all of the incompatible donated cells disappeared from the recipient’s circulation within the first thirty to ninety minutes following transfusion. The probable mechanisms and relative importance of intra- and extravascular destruction of erythrocytes are briefly discussed.

4. Destruction of recipient dogs’ corpuscles by donated immune plasma was relatively slow, and spherocytosis and increased osmotic fragility of the recipients’ cells were evident for periods as long as twenty days. These observations are compared with those made in human beings after transfusions of plasma and of blood from dangerous universal donors.

5. The titer of complement in the sera of recipient dogs was sharply reduced for at least five hours after all transfusions of incompatible whole blood, but isoagglutinin titers were less regularly reduced after such transfusions.

6. Other notations of interest included estimates of the concentrations of serum bilirubin, sodium and potassium, determinations of clotting time, prothrombin concentration, and observations on red cell morphology, intravascular erythrophagocytosis, and shifts in distribution of leukocytes and in the electrophoretic patterns of plasma.

ACKNOWLEDGMENTS It is a pleasure to acknowledge the technical assistance of Mrs. Jane Peters, Miss Mary Jane Izzo and Miss Shirley Deshon.