Specimens of ovarian cancers, which were obtained through laparotomy from 17 patients who received no preoperative chemotherapy and were examined histopathologically, were immunohistologically stained with anti-PCNA antibody to examine the ability to proliferate. The percent age of stained tumor cells per 1,000 cells was used as a PCNA-labeled rate. This rate was analyzed in relation to the clinical stage/histological type and the presence or absence of lymph node metastasis. 1. Tissue specimens were stained with anti-PCNA antibody in all cases, and the PCNA-labeled rate was 49.5 +/- 13.3%. 2. There were no significant differences in PCNA-labeled rates between different histological types or between clinical stages. 3. The PCNA-labeled rates was significantly higher in cases with metastasis than in those without metastasis (p < 0.01). 4. No metastasis was detected in the cases showing a PCNA-labeled rate of 50% or below. It was indicated that this PCNA-labeled rate, which can be determined with formalin-fixed specimens, is useful for evaluating the degree of biological malignancy of ovarian cancer.