To the bone marrow of aplastic anemia and normal persons, being cultured by means of clinical tissue culture method, RNA and DNA at various concentrations were added directly to the media to see their effects on the leucoyte and platelet series. The following are the results. 1. As for the leucocyte series of normal human bone marrow, the addition of RNA as well as DNA at optimal concentration showed an increase in the growth area and cell density, while in the case of neutrophils their wandering velocity was accelerated. In the case of aplastic anemia human bone marrow the addition of both RNA and DNA at optimal concentration likewise showed a stimulating action on the leucocyte series, and this effect was further enhanced when VB12 was added concomitantly. 2. As regards the platelet series in culture, the addition of RNA and at optimal concentration acceraded the function of megakaryocytes in both bone marrow of normal persons. and aplastic anemia. 3 The stimulating effect of RNA on the platelet series was stronger than of DNA, but the effect of the two nucleic acids on the leucocyte series did not differ significantly.