A study was made to determine wheter or not bone marrow scintigraphy with /sup 111/In chloride delineates the real distribution of hematopoietic cells. In a patient with acute myelogenous luekemia at the stage of complete remission, there was a significant incorporation of /sup 111/In into bone marrow cells (20 - 28% compared with 6% in the controls). Incorporation of /sup 111/In into peripheral blood cells was 0 at after 10 hours and 5% to 6% after 7 days. The plasma disappearance curve of /sup 111/In consisted of 2 exponential components, one with a half-life of 6.5 to 9.5 hours followed by a slow component with a half-life of 20 to 30 hours. 5 to 7% of the injected dose was excreted in the urine in 24 hours. The distribution of active marrow was investigated with bone marrow scintigraphy in various hematological disorders and the results were compared with those obtained with sup(99m)Tc sulfur colloid. The results obtained in this study suggest that /sup 111/In is incorporated into erythroid precursors, and that this property of /sup 111/In makes in an ideal bone marrow scanning agent for observation of real hematopoietic bone marrow distribution in blood disease.