AIM: IL-12 acts upon T lymphocytes and activates its receptor complexes of ?1/?2 ,and so IL-12 can regulate TH1/TH2 balance. Our study is aimed at IL-12-inducing apoptosis of T cells and expression and signal conduction of Bcl-2 during T cell apoptosis. METHODS: The apoptosis of T cells was detected by Annexin V staining cytometry and the expression of Bcl-2 under different inhibitors were detected by the method of semi-quantitative PCR. RESULTS: IL-12 can induce the human leukemic T cell line(TIB-152) and the human lymphoma T cell line(HTB-176) and the normal human T cells to undergo apoptosis. The Bcl-2 expression at 6 hours of treatment with IL-12 increased aparently,and reached the max at 24 hours. But IL-12 did influence Bcl-2 expression. IL-12 can induce T cells to undergo apoptosis which is characterized by early membrane changes. CONCLUSION: The inducing effect is correlated with the concentration of IL-12 and the maturation of T cells. Bcl-2 takes part in the progression of T cells' apoptosis as a apoptosis mediator.