Concanavalin A (Con A)-activated cells were fractionated by separating cells that agglutinate with peanut agglutinin (PNA) which binds preferentially to the sugar sequence beta-D-Gal-(1 leads to 3)-D-GalNAc. PNA-agglutinable cells were found to exert a significant suppressor effect on the primary antibody response to sheep red blood cells, whereas PNA-nonagglutinable cells did not affect the antibody response. It was also found that PNA-agglutinable suppressor cells were sensitive to treatment with anti-Thy 1.2 and complement (C), anti-I-J antiserum and complement, and anti-Ly 2.2 antiserum and complement. These results suggest that the PNA-agglutinable suppressor cells, separated from Con A-activated cells, were T cells and that these suppressor T cells possess abundant beta-galactosyl residues exposed on the cell surface, not masked by sialyl residues. Furthermore, it was found that antigen-specific suppressor cells were also separable by use of the agglutinability with PNA. The PNA-agglutinable suppressor T cell activity was eliminated by treatment of the Con A-activated PNA-agglutinable cells with anti-asialo GM1 and complement, anti-Forssman antiserum and complement, and anti-globoside antiserum and complement, but not by treatment with anti-GM1 antiserum and complement. Conversely, the helper T cell activity that was induced by Lens culinalis agglutinin and separated by Limulus polyphemus agglutinin, was eliminated by treatment of the cells with anti-GM1 and complement, but not by the treatment with the other anti-glycolipid antisera and complement.