Nonirradiated B-lymphocyte-deficient CBA/N mice given T6T6 chromosome-marked normal CBA/CaHN spleen cells became lymphoid chimeras exhibiting donor-type mitoses. Normal CBA/CaHN recipients did not exhibit significant numbers of donor-type mitoses. The lymphoid cell chimerism in the CBA/N host appeared in spleen, lymph nodes, and Peyer's patches, but not in marrow or thymus. Stimulation of CBA/N-recipient spleen cells in vitro suggested that the chimerism involved donor T6T6 cells which were responsive to the B-lymphocyte mitogen, lipopolysaccharide, but not to the T-lymphocyte mitogen, phytohemagglutinin. These data indicate that stable, long-term chimerism of a specific class of lymphocytes is possible in nonirradiated, B-lymphocyte-deficient CBA/N mice.