1. Resistance of erythrocytes to hyptonic salt solusion is decreased when erythrocytes are treated with trypsin. 2. Erythrocytes, even treated with trypsin, have yet antigenity. 3. Forssman's antibody and Forssman's lipoid antibody react well with bovine erythrocytes treated with trypsin in hemolytic and hemagglutinic reactions. 4. Forssman's antibody is not absorbed by normal bovine erythrocytes, but well absorbed by bovine erythrocytes treated with trypsin. 5. When anti-serum, got from rabbit immunized with bovine erythroeytes treated with trypsin, is absorbed by guinea-pig's kidney salt emulsion and its kidney lipoid, hemolysin for goat's and sheep's erythrocytes is absorbed. 6. When anti-serum, got from rabbit immunized with bovine erythrocytes treated with trypsin, is given to guinea-pig intravenously, the guinea-pig shows inverse anaphylaxis, but the phenomenon is not seen by injection of ordinary bovine hemolysin.