Marrow stem cells from old and young donors have often been compared by measuring concentration and numbers of CFU-S in mice. However, little information is available on hematopoietic stem cells in elderly people. This present study was undertaken to investigate age-associated changes in the concentrations of granulocyte-macrophage progenitor cell (CFU-C) and erythrocyte progenitor cell (CFU-E) in human bone marrow. We examined CFU-C from 101 subjects and CFU-E from 26 subjects by age, ranging from 28 to 95 years, and found there was no difference in the concentration of CFU-C but a slight decrease of the concentration in CFU-E in elderly subjects.