The study was carried out on CBA mice using the method of heterotopic transplantation. A fragment of the femoral bone marrow (1/2) or spleen (1/5 of the organ) was transplanted under the renal capsule of a recipient. The following donor-recipient cross-transplantation variants were studied: young → young (Y → Y), young → old (Y → O), old → old (O → O), and old → young (O → Y). Cell suspensions were prepared from 2-month transplants inoculated in monolayer cultures and the cloning effi ciency (ECF-F) of stromal precursor cells (CFC-F) was evaluated. The bone marrow transplant ECF-F and the count of CFC-F in the O → O group were 8-fold lower than in the Y → Y group. In the O → Y group, ECF-F was 3-fold higher than in the O → O group, but by 2.5 times lower than in the Y → Y group. ECF-F in Y → O group was 2-fold lower than in Y → Y group. The ECF-F and CFC-F count in spleen transplants in the O → O group were 4- and 6-fold lower, respectively, than in Y → Y group. However, in O → Y group ECF-F was 7-fold higher than in O → O group and higher than even in Y → Y group. The weight of induced ectopic bone tissue after transplantation of the osteoinductor (fragments of the allogenic urinary bladder mucosa) was 2-fold lower in the O → O vs. Y → Y group. However, comparison of the ectopic bone tissue weights in different experimental groups showed that osteoinductor activity of the bladder epithelium did not decrease, but increased 3-fold with age (O → Y:Y → Y). A 5-fold reduction of this proportion in groups where the osteoinductor was transplanted from old donors to old and young recipients (O → Y:O → O) could be attributed to age-specifi c reduction of the count of inducible osteogenic precursor cells (IOPC). The data in general suggest that age-specifi c reduction of the stromal precursor count and functional activity could be caused by the true reduction (exhaustion) of cell pool (bone marrow CFC-F; presumably, IOPC) and by the regulatory effects of the organism (bone marrow and splenic CFC-F, IOPC). These data seem to be signifi cant for understanding of the role of osteogenic stromal precursor cells in the development of age-associated bone tissue defects, for example, senile osteoporosis.