A phase II study of carboplatin was conducted in ovarian cancer by a cooperative study group consisting of 22 institutions nationwide. The overall response rate of 50 evaluable cases was 38.0%. The response rate in cases with no prior chemotherapy was 54.2% and that with prior chemotherapy was 23.1%. In addition, the response rate was 26.3% in cases that received prior CDDP-based chemotherapy. Histologically, the response rate was high in serous cystadenocarcinoma and endometrioid adenocarcinoma. Hematologic toxicities, particularly leukopenia and thrombocytopenia, were frequently observed, but well tolerated, while renal and neurologic toxicities were rare. These results suggested that carboplatin is useful in the treatment of ovarian cancer.