We studied hemopoiesis- and immunopoiesis-restoring activity of small intestinal epitheliocytes in lethally irradiated mice. The populations of peripheral blood cells and parameters of humoral and cellular immune response in lethally irradiated mice returned to normal 6 months after transplantation of cells from the small intestinal epithelial layer. Study of the distribution of intestinal cells in the body after transplantation showed long-term persistence of the donor cells in tissues of lethally irradiated animals. These data attest to high hemopoietic potential of small intestinal cells.