The results of hematological studies in Nagasaki on atomic bomb (A-bomb) survivors which were carried out at Second Department of Internal Medicine from 1946 to 1956 have been brought for summary. 1) Anemic and leukopenic tendency revealed in the exposed in 1946 and 1947 has recovered as time went on, no difference being noticed in 1948 in cases of leukopenia and in 1956 in cases of anemia comparing with the control. 2) The incidence of eosinophilia in the exposed showed a characteristic variation from 1947 to 1953,which may be related to the A-bomb radiation. However, in 1956, no difference was noticed between the exposed and control. 3) In general, the tendency of restoring to normal values was extremely strong in the exposed in each item of investigation. Accordingly, so far as concerned with peripheral blood, no significant difference was observed between the exposed and control in 1956. 4) However, the clinical investigation of bone marrow in the exposed performed in 1956, still suggested a possibility of maturation arrest of granulocytic and megakaryocytic series in the short distance exposed. 5) Three cases of chronic myelocytic leukemia were found in these mass survey, two of them being in an early stage of the disease
