Amplification of the c‐ras‐Ki oncogene has been the most consistent finding reported in studies on oncogene activation in ovarian cancer, but for the most part the studies have been small and the results conflicting. In order to determine whether amplification occurred de novo in primary tumours or was associated with tumour progression and metastasis, 81 tumour samples from different sites in 26 patients with ovarian tumours and 7 xenografted ovarian tumour cell lines were assayed. Amplification of c‐ras‐Ki occurred infrequently and was apparent in a single metastatic site in a patient with poorly differentiated serous cystadenocarcinoma of the ovary. Ten‐fold amplification of the c‐ras‐Ki oncogene was also evident in a benign ovarian fibroma. Amplification of the c‐ras‐Ki oncogene is rare in ovarian tumours and does not appear to play a fundamental role in tumour development or progression.