Taxol is an antitumor drug which, as its mechanism of action, promotes microtubule assembly in vitro. Camptothecin (CPT) is an anticancer agent with the peculiar mechanism of poisoning eukaryotic DNA topoisomerase I. Both drugs are in clinical trials and their chemotherapeutic efficacy seems promising in refractory human ovarian cancer. We studied the molecular and cellular pharmacology of the two drugs when administered simultaneously toward human ovarian cancer cell line A2780. Taxol inhibits CPT-induced single-strand breaks as well as CPT-induced cytotoxicity. Taken together, our experiments indicate that the two drugs might interact with the same class of nuclear enzyme, i.e. DNA topoisomerase I.