By means of clinical culture method, the author added RNA and DNA at various directly to the media in which was cultured the bone marrow of normal rabbit, normal person, and aplastic anemia, with the purpose to see the effect of these nucleic acids on the erythropoiesis, and obtained the foliowing results, 1. The addition of RNA and DNA at optimal concentration to the bone marrow tissue culture of normal rabbit clearly accelerated erythropoiesis. 2. The addition of RNA and DNA at optimal concentration revealed a slignt accelerating effect of erythropoiesis of normal human bone marrow in tissue culture. 3. In the case of the bone marrow tissue of aplastic anemia patient, likewise the addition of RNA and DNA at opitimal concentration showed a slignt accelrating effect of erythropoiesis.