Immunocompetent cells obtained from NIP-RGG immunized mice were fractionated on bead columns coated with antigen or anti-immunoglobulin serum. The separated cell fractions were examined for their capacity to be stimulated by the antigen in short term culture, to produce antigen specific antibodies in the plaque assay and to bind radioactive labeled antigen. Cells which produce hapten specific antibodies or bind radioactive labeled hapten are removed from the cell population passed through a hapten-carrier complex coated column. Cells stimulated by the antigen to an increased DNA-synthesis are also retained by columns coated with the hapten-carrier-complex or the carrier alone; the fractionation seems to be carrier specific. The fractionation of cells is blocked by free antigen in the columnar fluid. However, the fractionation patterns of cells passed through anti-Ig-serum coated columns are different when antibody producing cells and cells stimulated by the antigen are compared. Whereas antibody producing cells and antigen binding cells are almost completely retained by anti-Ig-serum coated columns the cells which are stimulated by the hapten carrier complex are not removed from the passed cells. Studies to characterize the fractionated cell populations according to their sensitivity to anti-theta-serum, to the presence of Ig-receptors and to the phytohemagglutinin stimulation indicate that the antibody producing cells and the antigen binding cells have to be attributed to B-cells whereas the question whether the antigen stimulated cells are T- or B-cells cannot be definitely answered.