About 350 castrated male DS mice given testosterone propionate (TP, 100 micrograms/mouse/day) were grafted with androgen-dependent SC115 tumor or androgen-independent tumors (NHD with positive receptor; NHF with negative receptor). After 20 or 15 days, most of the developed tumors were excised and the mice were divided into 3 groups. TP injection was continued in one group and TP was stopped immediately or 20 days after the excision in the other groups. The cumulative 120-day mortality after transplantation of SC115 tumor into mice was significantly lower in the immediate androgen removal group (10%, 6/59) than in the androgen-injected group (59%, 51/87) or the delayed androgen removal group (42%, 19/45). The cumulative mortalities in mice with androgen-independent NHD and NHF tumors in the immediate androgen removal groups (97 and 91%, respectively) were similar to those in the androgen-injected groups (90 and 95%, respectively). All non-operated and TP-injected mice grafted with SC115 and androgen-independent tumor died due to the tumors within 50 and within 30 days after the transplantation, respectively. These findings suggest the usefulness of adjuvant endocrine therapy for preventing the recurrence of hormone-dependent tumors.