Colony-forming activity of bone marrow cells in 3- and 12-month-old Wistar rats does not differ by the number of early and erythroid precursors and by the formation of granulocyte-macrophage colonies. In senescence-accelerated OXYS rats, the number of early and erythroid precursors significantly increases by the age of 12 months and surpasses the corresponding values in Wistar rats. The number of granulocyte-macrophage colonies in OXYS rats does not change with age, but the numbers of these colonies formed at the age of 3 and 12 months in these animals are higher than in Wistar rats. As a result, the total number of hemopoietic colonies in 12-month-old OXYS rats 2-fold surpassed that in 12-month-old Wistar rats. Activation of granulopoiesis and increased numbers of early and erythroid precursors indicate deep changes in the functional status of the hemopoietic stem cell in 1-year-old OXYS rats in the direction characteristic of aging animals.