Human ovarian carcinomas (n = 215) were xenotransplanted into thymus-aplastic female nu/nu mice (NMRI). Growth of transplants was defined as take-off rate, growth rapidity, and feasibility of passages. In 204 cases these growth characteristics could be correlated with survival time of the individual tumor-donor patients. It could be shown that median survival time of patients without take-off was longer than with take-off. In the same way there was a significant difference between slow- and fast-growing transplants as well as in tumors with only one animal passage and with more than three passages. A life table analysis similarly shows that a good growth of a xenotransplanted human ovarian carcinoma into nude mice is correlated with a poor prognosis of individual patients. It could be demonstrated that at least in ovarian cancer growth of xenotransplants in nude mice indicates a prognostic significance.