Human T lymphocytes (CCTC) have been maintained in continuous culture by a new method. The ability of CCTC to produce three types of T cell response has been determined and compared to the published responses of T cells grown in 'T cell growth factor' (TCGF) medium. Unlike TCGF cells, CCTC will not give proliferative responses when stimulated with PHA, Con A, or allogeneic lymphocytes even when supplemented with autologous PBL as a source of accessory cells. Instead, CCTC are potent inhibitors of the proliferative response of normal cells in MLC. This suppressive activity is not specific for histocompatible cells. Finally, CCTC express cytotoxic activity to a number of human lymphoid cell lines and this activity appears to be different from the polyclonal cytotoxicity reported for TCGF-maintained cells. Our method of long-term T cell culture therefore appears to grow cells with different properties from TCGF cells.