Case 1. A 67-year-old man was admitted to our hospital because of fever, diarrhea and abdominal pain. Hemoglobin was 10.7 g/dl, white cell count 6,900/microliters and platelet count 36.7 x 10(4)/microliters. Bone marrow biopsy showed non-lobulated megakaryocytes. The karyotype was 47, XY, +8, -16, 5q-, + mar. We have followed up this case without any special treatment except for red blood cell transfusions. The platelet count has increased to 70.9 x 10(4)/microliters. Case 2. An 84-year-old man was admitted to our hospital because of tinnitus and headache. Hemoglobin was 7.9 g/dl, white cell count 1,200/microliters and platelet count 22.5 x 10(4)/microliters. Bone marrow biopsy showed hypocellular marrow and non-lobulated megakaryocytes. The karyotype was 46, XY, 5q-. We have followed up this case only with red blood cell transfusions. The platelet count has increased to 68.9 x 10(4)/microliters. The hematological findings and clinical courses of the two cases were similar to those in the 5q-syndrome first described by Van den Berghe et al. in 1974. And these cases are important in relation to c-fms oncogene and hematopoietic abnormalities.