Uterine capacity to form cytoplasmic progesterone receptor was compared in ovariectomized golden hamsters at three months and 15-17 months of age. A dose-response test with 17beta-estradiol(E2) showed that the uterine content of progesterone receptor (pmole/uterus) was equal in young and old at all dose levels. However, heavier old uteri had less receptor per gm tissue. Old and young hamsters were mated, ovariectomized on day 7 post coitum and after two weeks, all were given the same dose of E2. Endometrium was separated from myometrium before analysis of progesterone receptor. Myometrium was analyzed for both estrogen and progesterone receptors. Myometrium of both groups had comparable levels of both receptors. The mean concentration of progresterone receptor (pmole/gm tissue) was higher in old endometrium. Some old animals with liver, kidney and adrenal disease had more endometrial reaction after E2 treatment. A few with low endometrial receptor levels had normal livers but at least one sterile uterine horn. There was, however, no general decline with age in intrinsic uterine capacity to form progesterone receptors.