Ovarian cancer is currently the most lethal gynecologic malignancy in Europe and the US. Platin analogues and paclitaxel demonstrate high remission rates, but unfortunately the efficacy of cytostatic agents is limited by the development of multidrug resistance (mdr). Clinical paclitaxel resistance is often associated with mdr1 overexpression. In a recent study, we introduced a highly specific quantitative real-time reverse transcriptase polymerase chain reaction for the quantification of mdr1 transcripts. In the present study, we demonstrate that primary tumor cells from patients with recurrent ovarian cancer overexpress mdr1. To evaluate mdr1 expression, we collected tumor cells from 77 ovarian cancer patients (13 chemotherapy-naive ovarian cancer, 64 recurrent ovarian cancer). Cancer cells were aspirated from 49 solid specimens (63%) and 28 ascitic fluids (37%). Subsequently, cancer cells were exposed in 221 short-term cultures either to blank medium (control) or to a single anticancer drug, cisplatin, doxorubicin or paclitaxel. The drug concentrations applied referred to clinical relevant doses. mdr1 mRNA expression was significantly higher in specimens from recurrent ovarian cancer incubated in paclitaxel than in specimens from chemotherapy-naive ovarian cancer. No significant differences were detectable between the mean value of mdr1 mRNA expression in tumor specimens from recurrent ovarian cancer incubated in cisplatin or doxorubicin. Differences within the untreated patients group were also not statistically significant. The result of this study confirms clinical observations, as well as in-vitro studies based on tumor cell lines, that paclitaxel resistance is correlated with mdr1 overexpression.