A high proportion of human mammary cancers contain a measurable amount of estrogen receptors. The presence of estrogen receptors correlates well with the response of patients to endocrine therapy, but not with their response to chemotherapy. However, receptor‐mediated chemotherapy should result in more selective and efficient treatment of receptor‐positive tumors. Several agents containing an estrogenic and a cytotoxic moiety have been synthesized in the past. It is not surprising that the affinity of these compounds for the estradioi receptor is very low, since most of them were synthesized before our knowledge of hormone receptor mechanisms.