The bone marrow tissues were cultured from normal adult and rabbit. The processes of phagocytosis were scrutinized in the cultured tissues of bone marrow. The results are as follow: 1) The majority of neutrophilic leukocytes such as myeloblast and promyelocyte but a few exceptions of myelocyte exhibited no phagocytosis. Active phagocytosis was displayed by the matured neutrophilic leukocytes more than by metamyelocytes. The pseudo-eosinophilic leukocyte of rabbit bone marrow was much weaker in its phagocytic activity than the neutrophilic leukocyte. 2) Usually no phagocytic behaviors were recognized in eosinophilie, basophilic-leukocytes, lymphocytes or erythroblasts. 3) Remarkable adsorption and phagocytosis of carbon particles were exhibited by throm-bocyte but the matured type of megakaryocyte had no phagocytic activity. 4) The phagocytic activity of monocyte was at first lower than that of neutrophilic leukocyte but gradually grew high until it surpassed the latter. This great phagocytic activity of monocyte was kept long until the end of observation. 5) The so-called "Makrophagen" showed the greatest phagocytic activiy of all the bone marrow cells. 6) In regard to the average degree of phagocytosis of matured neutrophilic leukocyte, different values were obtained from one growth zone to another. When the average degrees of phagocytosis in whole growth zones were examined along the radial direction from marrow fragment, they exhibited the highest value after 3 hours’ cultivation. Thereafter the phagocytic activity of neutrophilic leucocyte again fell down. Pseudo-eosinophilic leukocyte showed its highest value of the average degree of phagocytosis after 6 hours’ cultivation. 7) Lowerings of phagocytic activity were observed when Nitromin or P(32) were added to the medium and these lowerings of activity were nearly proportional to the concentrations of these substances. This seems to point out some part of considerable importance which underlies the functions of bone marrow.