Murine lymphoma [SL2 and TLX9] cells were lysed by using an allogeneic or a xenogenic (rat) antiserum and antibody-dependent effectors from mice and rats. Murine spleens were poorly antibody-dependent effectors against this target. The peritoneal cavities of mice were a good source of effectors. In rats, the spleen contained effectors; adherent cells from the peritoneal cavity were comparatively ineffective. Cells from rat and murine spleens lysed sheep erythrocytes in conjunction with an appropriate antiserum. There is a difference in the antibody-dependent lysis of erythrocytes compared to nucleated mammalian cells. The distribution of antibody-dependent effectors is species dependent.