Cytokine-induced killer (CIK) cells are ex vivo expanded T cells with natural killer cell phenotypes and functions. In this study, the anti-tumor activity of CIK cells against hepatocellular carcinoma was evaluated in vitro and in vivo. In the presence of anti-CD3 antibody and IL-2 for 14 days, human peripheral blood mononuclear cell population changed to heterogeneous CIK cell population, which comprised 96% CD3(+), 3% CD3( inverted exclamation mark(c))CD56(+), 32% CD3(+)CD56(+), 11% CD4(+), 75% CD8(+), and 30% CD8(+)CD56(+). CIK cells produced significant amounts of IFN-gamma and TNF-alpha; however, produced only slight amounts of IL-2, IL-4, and IL-5. At an effector-target cell ratio of 30:1, CIK cells destroyed 33% of SNU-354 human hepatocellular carcinoma cells, which was determined by the (51)Cr-release assay. In addition, a dose of 1x10(6) CIK cells per mouse inhibited 60% of SNU-354 tumor growth in irradiated nude mice. This study suggests that CIK cells may be used as an adoptive immunotherapy for patients with hepatocellular carcinoma.