Age changes of stromal precursor cell (CFU-f) numbers and their cloning efficiency (CFE-f) in monolayer cultures were evaluated using the mathematical gradient decrease method in the bone marrow of mice, guinea pigs and rats. It was found that aging was accompanied by a decline of CFE-f and CFU-f numbers in all animal species studied. However, these changes were variable in different species, that could possibly be explained by species-related physiological characteristics and aging peculiarities. Since the population of bone marrow CFU-f is known to include committed osteogenic precursor cells, these findings indicate the possibility of age-related decline in the numbers of this cell type, which could be one of the reasons of osteoporosis of aging. The application of a mathematical gradient decrease method allows to predict the course of age changes and to evaluate the dynamics of CFU-f numbers and of CFE-f in association with organism aging.