The spleen (2/3) was removed in CBA male mice (the 1st group); in the 2nd group the bone marrow from the right posterior shin was removed. The hemopoietic splenic colonies were counted on the 8th day after the lethal irradiation and injection of 1 X 10(-6) nucleated cells of the intact spleen. A significant increase of the number of colonies in comparison with their number in control intact mice was observed. The authors suppose that this increase could also be caused by the local influence of the regenerating stroma of the spleen and by some stimulating factor discharge by the regenerating hemopoietic tissue.