Nitromiphene (NIT; CI 628) is a triarylethylene antiestrogen shown to be effective in treatment of experimental breast cancer. Nitromiphene is one of the earliest nonsteroidal selective estrogen receptor modulators (SERMs). It is an anti-estrogen capable to translocate the estrogen receptor to the nucleus and to induce the replenishment of the cytosol receptor. Nitromiphene inhibited the uptake of [3H]-estradiol in rat whole homogenates and isolated cell nuclei tissues and the pituitary, and inhibited estradiol-induced female sexual behavior. Nitromiphene has thus been shown to suppress the growth of chemically induced and ransplantedmammary tumors in rodents. Also, Nitromiphene was shown to have potent, prolonged antiuterotropic effects in immature rats. Nitromiphene has been shown to undergo conversion to demethyl Nitromiphene (CI628M), a phenolic metabolite which had greater affinity for estrogen receptors and greater biological potency in vitro than did Nitromiphene. However, the in vivo antiestrogenic effects of Nitromiphene and demethyl Nitromiphene were similar, possibly due to facile O-demethylation of the former compound after administration.