Some aminoacids could accelerate erythropoiesis of the bone marrow, especially the synthesis of hemoglobin. But aminoacids are not used as the components of hemoglobin, but they play a roll as the hemoglobinsynthesis accelerating factor. And the acceleration of hemoglobinsynthesis was extreme by addition of phenylalanine, tryptophane, histidine or valine. Cysteine, leucine, isoleucine, methionine, Paniltin or Minophagen C showed no effects.