Analogous to breast cancer, the expression of estrogen receptors (ER) by human ovarian cancers is thought to be of prognostic significance. This prospective study was designed to evaluate the ability of immunohistochemistry (IHC) for ER to define prognostic subgroups in this disease and to possible characterize the group of patients that would benefit from ER analysis. The IHC technique for localising ER was published by Press and Green (1984). In IHC the percentage of cells stained was determined as well as the staining intensity that was graded on a 4 step scale. Tissue from the primary focus of 61 ovarian cancers was sampled during surgery and frozen immediately. FIGO Stage 1 disease was observed in 7 patients, stage 2 in 2, stage 3 in 36 and stage 4 in 16 women. Tumours of histological grade 1 were found in 3 cases, grade 2 in 20 and grade 3 in 38 specimen. Serous carcinoma was diagnosed in 43 lesions, mixed cell types in 10, mucinous and endometrioid each in 4. Minimal follow-up was 8 years. Statistical analysis was performed using the Wilcoxon Rank and Log-Rank test of Kaplan Meier curves. The median survival was 10.62 +/- 1.83 years for stage 1, 5.83 +/- 0.39 years for stage 2, 2.38 +/- 0.39 years for stage 3, and 3.71 +/- 0.76 years for stage 4. Tumour stage (p < 0.05), grade (p < 0.05) and cell type (p < 0.01) were predictors of survival. Age was of borderline significance (p = 0.058). The relative amount of stained cells was no predictor of prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)