It is valuable for the research of pathological anatomy to detect the distributions of active hematopoietic organ in the patients with various blood dyscrasias. (99m)Tc sulfur colloid was applied on 5 normal subjects as a control and 7 patients with hypoplastic anemia using a Type Ⅲ gamma scintillation camera (Nuclear Chicago Ltd.), for studying the distribution of active hematopoietic bone marrow. After 30 min. of intravenous infusion of 5 to 10 mCi of (99m)Tc sulfur colloid, a black and white polaroid film (ASA 3000: 3000 speed/107 type) was exposed under the 1000 hole multicollimeter of the Type Ⅲ gamma scintillation camera total counts were adjusted to be 1-5x 10(4). Blood picture was examined periodically. And, among these date, one considered the results to be most appropriate which were obtained on the closest date when the patient was studied for the distribution of (99m)Tc sulfur colloid. The (59)Fe-ferrokinetics were performed using a modified method of Pollycove and Hoffe. In normal subjects, the active hematopoietic bone marrows, namely the positive uptake of (99m)Tc sulfur colloid, was distributed in the skull, sternum, thoracic and lumbar spines, pelvic bone, femur and humerus. The positive uptake was also occasionaly obtained in the joints of both elbow and knee, in contrast to the bones of foot and hand. The intensity of the figures was higher in the proximal part of tubular bone than in the distal part. The distributions of active hematopoietic organs in the patients with hypoplastic anemia were classified as follows depending on the intensity and figure of (99m)Tc sulfur colloid uptake. Type Ⅰ was a narrow distribution of the diffuse and obscure figure. This Type Ⅰ was subclassified further: In Type Ⅰa, active marrow was scarcely figured out. In Type Ⅰb, active marrow was figured out more widely than in Type Ia although its image was obscure and diffuse. And in Type Ⅰc, the active hematopoietic marrows was restricted only in the vertebrae with clearer uptake of (99m)Tc sulfur colloid. Type Ⅱ is the narrow islet form with clear and distinctive high density figure and with the obscure and lowd ensity in background. Hypoplastic anemia showing Type Ⅰ figure belonged to the Types Ⅱ and Ⅳ according to the classification made in our Department. This demonstrated a typical hematological findings of hypoplastic anemia with a pancytopenia in the peripheral blood, hypocellularity in the bone marrow, a prolongation of plasma iron disappearance time (PIDT), and decrease in percentage red cell utilization (%RCU) in (59)Fe-ferrokinetics, and low uptake of (59)Fe into the bone marrow. On the other hand, the patient showing Type Ⅱ figure belonged the Type Ⅰ of hypoplastic anemia in our classification. This demonstrated a hypercellularity in the bone marrow, relatively normal %RCU in (59)Fe-ferrokinetics, and prolonged retention of (59)Fe uptake in the bone marrow.