The usefulness of spleen scans in the selection of an area of the spleen for further radiation therapy in a refractory patient with chronic myeloid leukemia is demonstrated. Estimation of the degree of reduction of spleen size in response to treatment of patients with chronic myeloid leukemia, Hodgkin's disease and polycythemia vera is described as is the disappearance of a Hodgkin's mass following endoxan therapy. The value of spleen scans in detecting the presence or absence of splenomegaly in cases of polycythemia vera without a palpable spleen is also discussed