[Changes in the female gonads of the chick embryo after tamoxifen]

Tamoxifen has been given to Chick embryos between the 3rd and 7th day at doses of 0.2-2 mg/egg. It was non-toxic and strongly anti-estrogenic. The female gonads were modified in their development. The ovary showed dense medulla with numerous cords and a reduced cortex. The right gonad partially regressed and was "masculinized". Mullerian ducts normally regressed in tamoxifen-treated male embryos. These results suggest the physiological intervention of estrogen during the normal embryonic female development.