The total content of putative estradiol-specific cytosolic type I and nuclear type I and II estradiol-specific binders was measured in 8- and 9-day-old male and female chick embryo Mullerian ducts. Cytosolic and nuclear type I estradiol-specific binding levels were similar in males and females, and no significant differences were noted among right vs. left and 8-day-old vs. 9-day-old embryo Mullerian ducts. The levels of nuclear type I estradiol binder were consistently higher than the cytosolic type I binder, but this difference was not significant. Nuclear type II estradiol-specific binding, however, was significantly higher in the left Mullerian ducts of both male and female embryos. The significance of these findings in relation to the regression of Mullerian ducts in male and female chick embryos is discussed.