The influences of 1) the sera of the patients with various blood diseases, 2) aminoacids, and 3) vitamins, on the rabbit bone marrow culture in fluid were observed. Ⅰ. The influences of the serum a) By addition of any sorts of serum, there were no increase of nueleated cell. This fact might be caused, i) in general, by the ripening of a great number of erythroblasts into normal erythrocytes, and ⅱ) in some blood diseases, by the depressive action of some factor contained in the serum. b) Erythrocytes increased in number, especially by the exist of the serum of healthy individual, but the serum of the patient with hypoplastic anemia or Banti’s syndrome arrested the increasing of erythroeytes. c) Without serum hemoglobin could not be synthesi...