The high incidence and mortality of breast cancer and other estrogen receptor related tumors motivates efforts to develop innovative imaging probes to effectively diagnose, evaluate the extent of the tumor, and predict the efficacy of treatments while concurrently and selectively delivering anticancer agents to the cancer tissues. In the present study, 1-[2-(cyclopentadienyltricarbonyltechnetium-99m)-2-oxo-ethoxy-phenyl]-1,2-di-(p-hydroxyphenyl)but-1-ene was prepared and investigated as a potential agent for imaging estrogen receptors (ERs) in associated tumors. The compound was obtained in high 2 radiochemical purity and radiochemical yields. The biodistribution of the radioactive compound in mature female rats showed an ER-mediation in the ovarian target tissues as the uptake was reduced by a blocking dose of estradiol. The nonspecific uptake in muscle was relatively low.