The in vitro antitumor activity of a novel ginseng saponin metabolite, 20-O-β-d-glucopyranosyl-20(S)-protopanaxadiol (IH-901), was examined against four human cancer cell lines and one subline resistant to cisplatin (CDDP). The growth inhibitory activity of the compound was estimated by MTT tetrazolium assay. The mean concentrations of IH-901 needed to inhibit the proliferation of the cells by 50% (IC₅₀) were 24.3, 25.9, 56.6 and 24.9 μM against human myeloid leukemia (HL-60), pulmonary adenocarcinoma (PC-14), gastric adenocarcinoma (MKN-45) and hepatoma (HepG2) cell lines, respectively. These values are higher than that of CDDP. In the CDDP-resistant PC/DDP cell line, the IC₅₀ values of IH-901 and CDDP were 20.3 and 60.8 μM, respectively. These results suggest that IH-901 is not cross-resistant to CDDP in this cell line and could be a candidate for the treatment of CDDP resistant pulmonary cancer.