Ovarian carcinomas are known to rapidly develop drug resistance against chemotherapeutic agents. This phenomenon is often associated with the expression of pl70-glycoprotein. A high rate of transcription of the corresponding mdr1-gene in resistant tumors is reported. Amplification of the mdr1-gene has been observed in tumor cell lines exposed to cytotoxic drugs; however, significant information is lacking as to whether this holds true in clinical carcinomas. To fill this gap, we investigated the rate of gene amplification of the mdr1-gene in 63 recurrent ovarian carcinomas and we determined the resistance pattern of these cells using an ex vivo assay. The tumors showed varying ex vivo resistance patterns which did not correlate to clinical parameters. Amplification of the mdr1-gene was not observed in any of the cancer specimens. Therefore, we conclude that mdr1-gene amplification is not a common pathway for the development of chemoresistance in clinical ovarian carcinomas.