Cytokinetic effects of cisplatin on human ovarian cancer cell lines with natural cisplatin-resistance was examined by means of flow cytometry. These ovarian cancer cell lines derived from patients with clear cell carcinoma and serous cystadenocarcinoma were established and designated "KK" and "MH", respectively. Both KK and MH cells have shown resistance to cisplatin and IC50 of them were 0.95 microM and 3.28 microM, respectively. Cisplatin inhibited cell cycle progression at G2 +M phase up to IC50 of each cell from the analysis of cell cycle. Similar results had been obtained in the case of "KF" cell which was sensitive to cisplatin. Further studies of these cells should be performed to elucidate the mechanism of cisplatin resistance.