The survival of implanted tumor cells in mice which had been treated with ginseng saponin in combination with either adriamycin or vincristine was evaluated. While the majority of tumor cells implanted into normal mice failed to surive(52.1 to 63.%), most of those implanted into mice which had been pretreated with either adriamycin or vincristine survived. If the mice were secondarily treated with ginseng saponin, the ability of adriamycin or vincristine to inhibit the survival of implawted tumor cells was restored within 24 hours. Restoration of tumoricidal activity by ginseng saponin treatment was more evident in the adriamycin pretreated mice. Peritoneal macrophages isolated from mice pretreated with both ginseng saponin and adriamycin had more increased tumoricidal activity, when compared with those isolated from mice treatcd with adriamycin alone. This ginseng saponin enhancement of tumoricidal activity was comparable to that obtained by treating mice with lymphokines, a product of PPD stimulated lymphocytes isolated from BCG treated mice. These results suggested that both adriamycin and vincristine may damage the macrophages required for the natural host defense machanism and allow the implanted tumar cells to survive. Ginseng saponin may, however, protect the macrophages from drug induced damage.