To study the clinical characteristics of ovarian endodermal sinus tumor, 22 patients with this disease who were managed at the Kurume University Hospital from 1970 to 1983 are analysed retrospectively. Before 1977 the patients received mainly radiation therapy as a postoperative treatment, and only two of 13 patients during this period survived. After 1978, multi-drug combination chemotherapy brought a remarkable improvement in the prognosis showing six survival cases out of 8 patients, and four of them are still alive with no evidence of the disease. Although the therapeutic efficacy of the combination of vincristine, actinomycin D and cyclophosphamide, or cis-diamminedichloroplatinum, vinblastine and bleomycin was evident as previously reported, half of the cases achieved a drug-resistance against these regimens during the first line therapy and this required a change in the program. Further, two drop out cases caused by the severe side effects of these aggressive treatment were noted. The best treatment for malignant germ cell tumors is not yet known, and a more effective and acceptable program is demanded to attain the goal of chemotherapy.