CD4⁺CD25⁺ and CD8⁺CD25⁺ thymocyte-derived T-cell clones suppress the proliferation in MLCs of CD4⁺CD25^- thymocytes. Suppression by CD4⁺CD25⁺ or CD8⁺CD25⁺, but not by CD4⁺CD25^- or CD8⁺CD25^-, T-cell clones of the proliferative response of autologous CD4⁺CD25^- thymocytes to allogeneic T-cell-depleted PBMNCs. On day 5, cells were harvested and their proliferation assessed by measuring ³H-TdR uptake.