Abstract The effect of several new dihydroepiandrosterone ester derivatives A2 – A6 was demonstrated using female cycling mice, which were synchronized for estrus with luteinizing hormone‐releasing hormone (LHRH) and injected with the steroids. The binding to the progesterone receptor (PR), was obtained from the cytosol of uteri from adult estrogen‐primed rabbits. A1 binds to the PR and inhibited the ovulation in cycling mice stimulated with LHRH. The activity of the endometrium and mammary glands in these mice was markedly reduced as compared to the control. A2 , A4 , and A5 were not active; nevertheless, A3 binds to the PR with high affinity. However, this steroid did not produce any effect as compared to that observed for the control in the endometrial and mammary glands. A6 binds to the PR with the highest affinity and induces a synergistic activity with progesterone in these tissues. Furthermore, A6 inhibited the ovulation in the same manner as A1 . These results suggested that A1 and A6 are blocking the gonadotropin secretion. A1 inhibited the conversion of progesterone to 5α‐progesterone. As a result of this, a blockage of the ductal and alveolar epithelial cell proliferation in the mammary and endometrial glands, which depends on 5α‐progesterone, was also observed.