In sublethally irradiated CBA mice, the relative and absolute numbers of spontaneous rosetts forming cells against sheep erythrocytes are markedly decreased in bone marrow. 2. The decrease of the absolute number of spontaneous RFC is also important in the spleen in spite of an increase of the RFC relative number above the normal values between the 8th and 12th day after irradiation. 3. The graft of normal bone marrow cells immediately after irradiation of the shielding of a medullary area during irradiation promotes the recovery of the immunocytoadherence capacity of the bone marrow cells but not of the spleen cells.