To investigate tumor angiogenesis in benign, borderline and malignant epithelial ovarian tumors and its relation with the pathogenesis of ovarian carcinoma, polycolonal antibody directed against human von Willebrand factor (factor VIII) was used to measure the microvessel density (MVD) in 66 cases (11 benign, 10 borderline, and 45 malignant) of epithelial ovarian tumors by using immunohistochemistry. The results showed that the mean MVD in epithelial ovarian cancer (31.7 +/- 11.2, 400 X) was higher than in benign and borderline tumors (16.7 +/- 6.3, 20.7 +/- 8.8 respectively, P 0.05). But there was significant difference in MVDs among those in different tumor stages (P < 0.05). MVD in stage III-IV cancer was higher than that in stage I-II (P < 0.05). It is concluded that the tumor angiogenesis is an early event in ovarian tumorgenesis. The increased tumor micovessel might be responsible for tumor development.