By lcading cortisone to the bone-marrow tissue culture of the rabbits subcutaneously injected with the serum of hypoplastic anemia or of Banti's disease successively for seven days and by observing the peripheral blood picture and the findings of the bone-marrow tissue culture of the rabbits previously given intravenous injection of 50mg/kg ACTH and then given subcutaneous injections of the serum of hypoplastic anemia successively seven times, the author obtained the following results. 1. Cortisone acts as to recover the lost erythropoiesis of the bone marrow of the rabbit injected with the serum of hypoplastic anemia. 2. Cortisone likewise possesses an action as to recover the lost erythropoietic function of the bone marrow of the rabbit injcted with the serum of Banti's disease. 3. In the case of (1) or (2) even when cortisone is loaded to the bone marrow culture in such a high does as to damage the bone marrow cells of normal rabbit, the erythropoiesis of the bone marrow has shown a tendency to recover. 4. In the case of the rabbit previously given ACTH injection and then successive injections of the serum of hypoplastic anemia. the peripheral blood picture shows hardly any anemia, and the erythropoiesis of the bone marrow is likewise not at all affected. 5. From these, it is clear that the stimulating action of ACTH or corisone on the bone-marrow erthropoiesis can counteract against the inhibitory action of anemia-inducing substances contained in the sera of these patients.