In the bone-marrow tissue culture of normal rabbits and normal persons, by performing vital staining of tissues with neutral red and lithium carmine, the author in vestigated the degree of staining in various bone marrow cells appearing in the growth zone of explant, and obtained the following conclusions: 1. Neutral red stains much more markedly than lithium carmine, and it has been found that neutral red is quite suitable for vital staining in observing bone marrow cells. 2. The stainability of pseudoeosinophils in the bone marrow in normal rabbits is far clearer than that of human neutrophils. 3. The stainability of each of various bone marrow cells appearing in the growth zone in bone-marrow tissue culture of normal rabbit reveals such a peculiarity that it make the differentiation of cells quite easy. 4. Investigating the degrees of staining by neutral red of pseudoeosinophils in rabbit bone marrow from the standpoint of time element, it has been found that staining of cells commences immediately after addition of dyes to the medium, reaching the maximum staining after about 5 hours' culture, but thereafter the stained color begins to fade gradually, and within 24-30 hours it loses its color completely.