Five novel Pt(II) complexes with some 2-cycloalkyl-substituted benzimidazole carrier-ligands were synthesized and evaluated for their in vitro cytotoxic activities against HeLa and OVCAR-3 cell lines. A cell viability test revealed that [dichloro-bis(2-cycloheptylbenzimidazole) platinum(II)] is less cytotoxic than cisplatin, and its cytotoxic effect can be compared with that of carboplatin. Flow cytometric analysis revealed that this complex at 117 mu M concentration causes apoptosis in approx. 72 % of the OVCAR-3 cell population. In addition, the complex was found to cause an increase in the SubG1 population of both OVCAR-3 and HeLa cells and to cause less apoptosis in HeLa cells than cisplatin.