Six months old ovariectomized female rats (n = 9) were treated with (-)deprenyl in a dose of 0.25 mg/kg s.c. three times a week, and (n = 9) with physiologic saline (0.1 ml/100 g) till decay. It was found that control females (n = 9) decayed within the age of fifteen months while the members of the (-)deprenyl treated group were all alive at that age. Moreover three (-)deprenyl treated female rats reached 36 months of age. Sexual activity was quite absent in both groups. The data suggests that (-)deprenyl extended the lifespan of female rats only in total absence of gonadal hormones and sexual activity.