In order to study the clinical efficacy of Ninjin-youei-to (Ren-shen-yang-rong-tang) the authors administered it to five cases of aplastic anema (AA) and two cases of primary acquired refractory anemia (PARA). It was found to be clinically effective in three of the AA cases and one case of PARA. The percentage of improvement of anemia and platelet counts were 43% and 57%, respectively, but no effects were seen on the white blood cell count. This suggested that the mechanism of effect of this Chinese herb was to not only stimulate the stem cell directy, but also to activate the stromal cells of the microenvironmental system indirectly.