The human tumor clonogenic assay (HTCA) and the human tumor xenograft system implanted in nude mice were performed simultaneously in an ovarian cancer patient as chemosensitivity testing. Eight anticancer drugs (5-FU, MMC, VCR, ACD, BLM, VLB, CDDP, and ADM) were applied to the HTCA and the human tumor xenograft system. In the HTCA, 5-FU and MMC were sensitive, VCR was moderately sensitive, and ACD, BLM, VLB, CDDP, and ADM were resistant. In the human tumor xenograft system, MMC, VCR, and ADM showed tumor regression (++), and CDDP, VLB, BLM, 5-FU, and ACD exhibited no response (-). Two of the three drugs, which were classified as sensitive or intermediately sensitive in the HTCA, showed tumor regression (++) in the human tumor xenograft system. And four of the five drugs, which were resistant in the HTCA, exhibited no response (-) in the human tumor xenograft system. Clinically, PVB therapy (CDDP, VLB, and BLM) was applied to the present patient, but after recurrence, 5-FU + MMC therapy was applied on the basis of the results of the HTCA. In addition, ADM was added with reference to the results of the human tumor xenograft system. As a result of this therapy, the tumor growth was inhibited. It is possible from the present data that simultaneous chemosensitivity testing of the HTCA and the human tumor xenograft system implanted in nude mice is very useful when choosing sensitive anticancer drugs.