A comparative exploration of the optimum regimens for CDDP and CBDCA therapy of malignant gynecologic tumors was conducted using both in vitro and in vivo approaches. In vitro, CBDCA exerted less cytotoxicity with short-time exposure, but over a longer time was as effective as CDDP. Pharmacokinetic studies demonstrated rapid binding of all administered CDDP to protein, while free-Pt was seen for many hours after CBDCA treatment. These results suggest that the gradual action of CBDCA leads to the appearance of cytotoxicity, and that in clinical use CBDCA affects the tumor cells for a long time. To increase the active dose of platinum, treatment with high doses of CDDP, or CBDCA, or the two platinum compounds with different pharmacokinetic behavior in combination, was designed for optimal therapeutic protocols. In the CDDP-alone treatment animals, renal toxicity was apparent with the increase in dose level. However, in the combination CDDP-and-CBDCA treatment animals, the total dose level could be elevated without causing toxicity. In the drug-sensitivity test, the combination therapy also exerted strong activity. The fact that the combined CDDP-and-CBDCA therapy appears to exert greater anti-tumor effects without any increment in adverse toxicity of these drugs is clinically promising.