Estrogens direct the development of the female genotype in embryogenesis and at puberty. Estradiol is the major estrogen secreted by the premenopausal ovary. Estradiol benzoate is an estradiol analog which contains a benzyl ester at the C-3 position. It is often used in combination with a progestin to induce estrus in domestic livestock. Estradiol benzoate binds to the human and murine estrogen receptor .alpha.