We report an autopsy case of acute erythremia which terminated in generalized infiltration of immature blasts similar to proerythroblasts. A 61-year-old man was admitted because of general fatigue and fever in June, 1990. Mild anemia and severe thrombocytopenia were noted. The bone marrow was hypocellular with 25.5% blasts similar to proerythroblasts and 36.5% erythroblasts, many of which were polynuclear and megaloblastoid. The blasts were cytochemically negative for POX, but positive for PAS staining. Therefore he was diagnosed as having acute erythremia. Partial remission was achieved by BHAC-EV therapy. But three months later, his marrow was replaced by 52.7% blasts as seen in admission. Those blasts were negative for lymphoid, myelocytic, megakaryocytic markers and antiglycophorin A, but positive for OKT 9. Electron microscopy revealed that some of blasts had characteristics of immature erythroblasts. In spite of low dose Ara-C therapy, he died of sudden gastrointestinal bleeding in December, 1990. The autopsy disclosed widespread infiltration of blasts, involving liver, spleen, lung, kidney and stomach. It was interesting that dysplasia had been confined to erythroid lineage throughout his clinical course. He seemed to be a rare case of blastic form of acute erythremia which should be distinguished from erythroleukemia.