1. Small particles essentially similar to those previously isolated from other tissues have been isolated from mammalian red blood cells (horse blood).
2. About one-third of the dry weight of the particles is lipids.
3. The particles produce hemolysins against the homologous erythrocytes when inoculated into a foreign species.
4. The fact that the particles can be isolated from mammalian red cells which do not contain visible granules is taken to indicate that some at least of the particles isolated from whole organs represent disintegrated "stroma."