A patient whose initial hematologic evaluation suggested the diagnosis of a microangiopathic hemolytic anemia (MAHA) was further evaluated and found to have erythroleukemia (DiGuglielmo's syndrome). This prompted us to review retrospectively the peripheral blood morphology of 12 patients with erythroleukemia. Anisocytosis, poikilocytosis, macrocytosis, and nucleated red cells have been described in patients with erythroleukemia; however, changes characteristic of a microangiopathic hemolytic process (schistocytes) have not been previously described. Our patients with erythroleukemia had prominent helmet and fragmented red cells, as well as elliptocytosis. Six of our 12 patients with erythroleukemia did not have blasts on their peripheral smear, and platelets were decreased (platelet count ranged from 2 to 92 X 10(3)/microliter), resulting in changes similar to patients with MAHA due to thrombotic thrombocytopenic purpura (TTP), traumatic RBC lysis, and disseminated intravascular coagulation. Our data indicate the RBC changes characteristic of MAHA are commonly seen in erythroleukemia, and that as many as half of these patients may not have white cell changes suggestive of leukemia on the peripheral smear. Patients presenting with microangiopathic hemolytic anemia require a bone marrow examination to confirm or exclude a myelodysplastic syndrome.