Abstract Human T-lymphocytes, after culture at 37°C for 48 h, suppressed the Con A-induced blastogenesis of fresh autologous lymphocytes. Both Fc γ receptor- positive and -negative T-cell subsets were active as suppressors. Non-T-cells failed to show such a phenomenon. Similarly, freshly isolated T-cells, and Fc γ receptor-positive T-lymphocytes also suppressed the blastogenic response. Thus, preculture is not required to obtain “suppressor cells”. The suppression of mitogen responses therefore seems to be an inherent property of T-cells.