In vitro cytotoxic activities of cisplatin combined with Chungpesagan-tang or puerarin, which were treated with or without human intestinal bacteria, were measured. When cisplatin was combined with Chungpesagan-tang and its ingredient treated without intestinal bacteria, they did not affect the in vitro cytotoxicity of cisplatin against tumor cell lines. However, when cisplatin was combined with intestinal bacteria-treated Chungpesagan-tang and its ingredients, the cytotoxicities against SNU C4, L1210, A549 and P388 tumor cell lines were synergistically increased. Puerarin, which was isolated from Puerariae Radix, did not show in vitro cytotoxicity. However, its metabolite, daidzein, showed potent cytotoxicity against tumor cell lines and was synergistic by the combined usage of cisplatin. These results suggest that natural glycosides are not only prodrugs which can be transformed to active compounds by intestinal microflora, but the combined usage of cisplatin with natural components, such as daidzein, and herbal medicinal polyprescriptions, such as Chungpesagan-tang, may be a new method for prevention and minimization of the toxicity of cisplatin.