The high affinity folate binding protein (FBP) is overexpressed in ovarian cancers. However, its role in the pathogenesis and biological behaviour of these neoplasms is not clearly understood. Using the monoclonal antibody (MAb) MOv 18 and cytofluorimetric analysis, we investigated FBP expression in frozen neoplastic tissues from 136 patients diagnosed with epithelial ovarian cancer. FBP values were compared with clinico-pathological characteristics (age, stage, histologic grade, histologic type, DNA ploidy, percentage of S-phase cells, and previous chemotherapeutic treatment). Some amount of FBP overexpression was observed in 122 of the 136 tumours examined. The overall mean value of FBP fluorescence index (FBP FI) was 5.6 (median 2.7; min 0.8--max, 78.9). By univariate analysis, FBP FI was overexpressed to a higher degree in ovarian neoplasms with high histologic grade, advanced stage, serous histology, aneuploid status, and high percentage of cells in S-phase. Of the total number (136) of cases, 106 had all the parameters assessed and were thus selected for stepwise selection procedure. The only significant independent variable was the percentage of S-phase cells, which accounted for about 31% of variance of FBP FI. Our results indicate that FBP is associated with parameters of biological aggressiveness in ovarian cancers.