Apes and Old World monkeys menstruate in a cyclic manner just as normal sexually mature women do. Edgar Allen,1Hisaw, Corner, Hartman, Morrell and others using castrated monkeys were able to produce endometrial growth followed by uterine bleeding after cessation of injections of theelin. It was desirable to know what effect theelin would have on castrated women. In a previous article we2described the effect of theelin injections on castrated young women whose uteri were intact. Endometrial hyperplasia was produced, as shown by histologic examination of tissue obtained by curettage before, during and at the end of the experiment. Bleeding from the uterus occurred both during treatment and within three to five days following cessation of injections. Activity in the breasts was characterized by a sensation of fulness, actual enlargement, tingling in the gland tree and erection of the nipples. The subjective symptoms that follow castration disappeared and