OBJECTIVE To explore the role of apoptosis-associated genes and caspase-3 activity in cisplatin (DDP)-resistant human ovarian cancer cell lines. METHODS The expressions of apoptosis-associated genes (bcl-2, bax, bcl-X(L) and bcl-X(S)) and the activity of caspase-3 were studied by reverse transcription-polymerase chain reaction (RT-PCR) and western blot in the cisplatin-resistant (A2780/DDP, COC1/DDP) and sensitive human ovarian cancer cells (A2780 and COC1). The apoptotic rates of A2780, COC1, A2780/DDP and COC1/DDP were measured with flow cytometry when treated with cisplatin. RESULTS The mRNA expressions of bcl-2 and bcl-X(L) in A2780/DDP cells were 1.87 +/- 0.25 and 1.73 +/- 0.15, and significantly higher than those in A2780 cells (P < 0.05), which were 1.48 +/- 0.14 and 1.41 +/- 0.19 respectively. The protein expressions of bcl-2 and bcl-X(L) in A2780/DDP cells were 1.99 +/- 0.11 and 1.69 +/- 0.16, and significantly higher than those in A2780 cells (P < 0.05), which were 1.51 +/- 0.17 and 1.28 +/- 0.11 respectively. The expressions of bcl-2 and bcl-X(L) in COC1/DDP cells were also significantly higher than those in COC1 cells (P < 0.05). While there was no significant difference in expression of bax between A2780/DDP and A2780 as well as between COC1/DDP and COC1. No expression of bcl-X(S) was detected. When cells treated with different concentration of DDP, the caspase-3 activities, apoptotic rates and PARP expressions in A2780/DDP and COC1/DDP were significantly lower than those in A2780 and COC1 (P < 0.05), which showed dose-dependent (P < 0.05). CONCLUSION Overexpression of anti-apoptotic genes and decrease of caspase-3 activity may relate to cisplatin resistance in human ovarian cancer cell lines.