The relatively high incidence of amplification and overexpression of the neu (c-erb B2/HER-2) oncogene in breast cancer, and its association with poor prognosis, particularly in node negative patients, may allow identification of patients who require aggressive therapy to prevent an early relapse. It's association with ovarian cancer, however, is less well defined than in breast cancer. An ELISA for the c-neu proto-oncogene related protein, p185, has been developed recently using the monoclonal antibodies NB3 and TA1. In the first study of it's kind, we assayed serum samples from patients with primary epithelial ovarian cancer for circulating c-neu p185. Elevated levels were found in 21/178 (11.8%) patients. No correlation was found between serum levels and either the presence or volume of tumor, when assessed either after primary or at second-look surgery. A change in c-neu p185 levels did not correlate with response to chemotherapy. When subjected to univariate and multivariate analyses together with other known prognostic factors, serum c-neu p185 was not a significant predictor of progression-free survival or overall survival. Although c-neu p185 may be involved in the pathogenesis of ovarian cancer, it's assay in serum has no value in prognosis or monitoring.