SummaryThe author reports a case of malignant erythroleucoblastosis with megalo-hlasts. Extreme immaturity of the red cell line was a notable feature in both the marrow and peripheral blood (subacute erythremia of Di Guglielmo). Very soon the number of myeloblasts increased in the bone marrow and in the peripheral blood and superseded the red cell line. Finally the patient died, presenting the typical picture of acute granulocytic leukemia.