Balb/c mouse spleen cells in vitro sensitized against ICR spleen cells were cultured in conditioned media(CM). The CM was produced by ICR spleen cells stimulated with Concanavalin-A(Con-A), and sensitized lymphoid cells were grown in CM. ICR mouse spleen cells were appeared to be a good generator of IL-2. Optimal growth was seen in growth medium containing 20% fetal calf serum. and 25% CM. When cultures were initiated at 1, 5, $10{ imes}10^4;cells/ml$, the cells were increased in numbers by about 20, 13, 5-fold, respectively, every 9 days. Such growth pattern was sustained for about 4-6 weeks and thereafter the cell growth was diminished gradually. Direct immunofluorescence indicated that 93% of the lymphoid cells grown in CM(for 10 days) expressed Thyl surface antigen. And the cells grown in CM were cytotoxic to the sesitizing ICR mouse spleen cells though cytotoxicity level was not high. According to these results, the cells grown in CM were considered to be cytotoxic T lymphocytes. The lymphoid cells grown for 20 days were nearly unresponsive to Con-A and therefore dependent only IL-2 to be used for IL-2 assay.