A new line of human serous cystadenocarcinoma of the ovary, designated OVA-5, has been established in athymic nude mice. A strong correlation was noted between tumor volume and plasma CA125 levels in mice bearing OVA-5 tumor. Growth of the OVA-5 tumor in castrated male nude mice was accelerated by s.c. administration of estradiol-17 beta and 5 alpha-dihydrotestosterone but not by progesterone. Estradiol-17 beta and 5 alpha-dihydrotestosterone also accelerated the growth of the OVA-5 tumor heterotransplanted into sialoadenectomized castrated male nude mice. No remarkable change was observed in the histological appearances of the tumors between control groups and hormone-treated groups. Receptor assays revealed that the OVA-5 tumor had both estrogen and androgen receptors. Growth of the OVA-5-tumor is thus responsive to estrogen and androgen.