Antibody production by normal mouse spleen cells in vitro requires the presence of both adherent and nonadherent cell populations. The data presented here demonstrate that by the addition of alpha-tocopherol (vitamin E) to the medium nonadherent spleen cells can be stimulated to respond to sheep red blood cells in the relative absence of adherent cells. In addition, alpha-tocopherol will enhance in vitro immune responses by populations of spleen cells containing both adherent and nonadherent cells.