In order to understand the nature of hormone-controlled embryonic sex organ differentiation, studies have been proposed to investigate the capacity of chick Mullerian duct cells to bind to several sex steroid hormones during the course of organogenesis. Tritiated estrogen, progesterone, or testosterone will be incubated with Mullerian ducts separately, and the binding of hormones to cytoplasmic and nuclear fractions of the duct cells will be assayed. The sucrose density gradient method will be applied to detect the hormone-receptor protein complex, and thus the time of appearance and the variety of hormone receptor protein complex will be investigated. The number of receptor proteins in the cytoplasmic fractions of different stages of duct development (Mullerian duct and oviduct) will be calculated from the dissociation constant between the hormone-receptor protein complex and its acceptor. Chromatin isolated from ducts (right and left) of different developmental stages will be incubated with hormone-receptor complex to investigate their relative capacities for accepting hormones. The possible changes of chromosomal components (acidic proteins) during differentiation will be measured by study of the rate of amino acid incorporation into acidic proteins, and the ratio of acidic protein to DNA in the duct chromatin. A comparison of RNA transcriptional capacity of the chromatin of the right and left Mullerian ducts at different stages of development will be made by incorporation of C14-UTP into RNA in the presence of E. coli RNA polymerase and ducts chromatin.