By means of bone marrow tissue culture devised in author's laboratory, the author has investigated the hematopoietic activity and white blood cell function (wandering velocity, phagocytosis of carbon particles and vital staining) in the bone marrow of 16 cases of patients of anchylostomiasis, which were classified into 3 groups according to the level of anemia. 1) Relative growth rate in hanging-drop culture was hardly lowered in most cases, but in a group of severe anemia with a slight decrease of the white blood cell count in peripheral blood, it being slightly lowered. 2) Wandering velocity of the neutrophils was hardly decreased in most cases, but in a group of severe anemia with a slight decrease of the whitebolod cell count, it being slightly decreased. 3) Phagocytosis of carbon particles of the neutrophils was hardly declined in a group of slight anemia, but along with a development of anemia in peripheral blood, it being fairly declined, especially in a group of severe anemia with a slight decrease of the white blood cell count. 4) As for the vital staining of neutral red, it was little altered in most cases, but in cases of severe anemia with a slight decrease of the white blood cell count, the neutrophils were stained relatively in the early stage and high degree, and discolored comparatively earlier than those of the control one. 5) Wandering velocity of the eosiuophils in the bone marrow was markedly accelerated in most cases with eosinophilia in peripheral blood, sometimes being more than 2 times those of the control one. 6) Increasing rate of the red blood cell count and hemoglobin content in fluid culture were slightly decreased, especially in groups of moderate and severe anemia. 7) According to the above-mentioned results, the author has confirmed that the hematopoietic activity and blood cell function in the bone marrow of anchylostomiasis were scarecely deteriorated and the development of anemia should be regarded as the results of blood cell arrest in the sinusoid of the bone marrow and deficiency of an iron supply to the hematopoietic tissues due to the disturbance of iron mobilization, and moreover the development of hypoplastic anemia in anchylostomiasis should be considered as a secondary occurrence following a long durated severe anemia.