To evaluate the anticarcinogenic effect and its mechanism of red ginseng, the mice were treated with red ginseng and received subcutaneous Bl6 melanoma cell line injection on the back. Tumor incidence was same (100%) both in water and red ginseng-treated groups, but tumor production was delayed in red ginseng-treated group. Survival time was somewhat longer in red ginseng-treated group. The histopathological findings were similar in both groups, but lymphocytic infiltration around the tumor and melanin production in the tumor cells were prominent in the red ginseng-treated group. Flow cytometric analysis on T lymphocytes and natural killer cells revealed increased $T_H$/$T_S$ ratio and increased NK cells in red ginseng-treated group. These results suggest that the anticarcinogenic effect of red ginseng may be exerted by the increased cell-mediated immunity and natural killer cell activity.