1. Two months after injection of rat bone marrow into lethally X-irradiated mice (950 r-RBM mice), 100% of the circulating RBC were serologically of the rat type, indicating that the surface molecular configuration of RBC from these experimental mice are of the rat type.
2. The hemoglobin was found to be also very much like the rat type in its ease in crystallization, its alkali denaturation property, its electrophoretic property, and its tendency to form a paracrystalline state at low temperature.
3. These cells possessed dual osmotic properties; the relative hemoglobin concentration released when cells were lysed in water was more comparable to the rat type, but its temperature dependency was more comparable to the mouse type.