Methyl protodioscin (NSC-698790) was a furostanol saponin isolated from the rhizome of Dioscorea collettii var. hypoglauca (Dioscoreaceae), a Chinese herbal remedy for the treatment of cervical carcinoma, carcinoma of the urinary bladder, and renal tumors for centuries. To systematically evaluate its potential anticancer activity, methyl protodioscin was tested cytotoxicity in vitro against human cancer cell lines by the NCI's (National Cancer Institute) anticancer drug screen. As a result, methyl protodioscin showed strong cytotoxicity against most cell lines from solid tumors with GI50 < or = 10.0 microM, especially selectively against one colon cancer line (HCT-15) and one breast cancer line (MDA-MB-435) with GI50 < 2.0 microM but moderate cytotoxicity was shown against leukemia cell lines with GI50 10-30 microM. The data are consistent with the fact that the rhizome of D. collettii var. hypoglauca has been employed for the treatment of solid tumors rather than leukemia in China for centuries. Based on an analysis using the COMPARE computer program with methyl protodioscin as a seed compound, no compounds in the NCI's anticancer drug screen database have cytotoxicity patterns similar to those of methyl protodioscin, indicating a potential novel mechanism of anticancer action.