The studies were conducted to investigate the combined effects of several combined preparation of crude drugs and mitomycin C(MMC). The combined effects on the proliferation of Molt-4 cells and activation of human lymphocytes were estimated by MTT colorimetric assays. The drugs itself enhanced the proliferation of Molt-4, but the inhibitory action of MMC was not affected by the combined treatment of the drugs and MMC. Among 9 kinds of the drugs, Sip Jeon Dae Bo Tang(SDT), Saeng Maek San(SMS) and Kwi Bi Tang(KBT) did not inhibit the action of MMC, but activated lymphocytes. When the mice were treated by MMC, the number of leukocytes was decreased significantly at the 1st day, but recovered at the 7th day. In the groups of MMC treated with SDT or KBT, the number of leukocytes was increased significantly than the group of MMC treated only at the 3rd day. The combined treatment of SDT, SMS and MMC retained the body weight of mice at the level of normal mice. The SDT, SMS and KBT did not change the number of plaque forming cells(PFC) and the proliferation of T cells. The combined treatment of SDT and MMC increased the number of PFC significantly than the MMC treated group. The combined treatment of SDT, SMS, KBT and MMC increased the T cell proliferation significantly than the MMC treated group. In conclusion, it is suggested that SDT, SMS and KBT can recover the side effects of MMC, such as weight loss, leukopenia and immunosuppression, without any intercalating the anti-proliferative action of MMC in vivo.