This study design is based upon in vivo data in order to: 1. Demonstrate the nuclear and cytoplasmic sites of estrogen and progesterone receptors in the mouse oviduct. 2. Compare the effects upon the number and locations of the receptor sites of cyclic endogenous estrogen and progesterone of mature mice and of exogenous ovarian hormones given to immature mice. 3. Provide basic data on sites of hormonal activities in the oviduct. 4. Determine the nuclear and cytosol binding sites by 3H-estradiol exchange. The techniques of dry-freeze, dry-mount, high resolution radioautography will be used to produce light microscopic autoradiographs. For the biochemical studies, the method of Katzenellenbogen will be used and will be limited to cytosol and nuclear receptors for estrogen for the study period.