Rabbit antibodies to cytoplasmic estrogen receptors (ER) of human breast carcinoma were utilized for investigating steroid-triggered in-vitro translocation of cytoplasmic ER to the nuclear compartment of the estrogen target cells. The immunofluorescent method (IF) previously described (S Raam et al., Eur J Cancer Clin Oncol 18: 1-12, 1982) was employed for immunohistochemical localization of ER. Four cases of normal endometrium, two cancers of the endometrium, and MCF-7 human breast cancer cells were maintained in a steroid free medium and exposed at 37 degrees C for two hours to growth medium alone (control) or to 2.5, 25 or 250 nanomoles of estradiol (E2), diethylstilbestrol (DES), or monohydroxytamoxifen (OH-TX). At the end of the incubation period the cells were processed for intracellular localization of ER. Complete traslocation of IF from the cytoplasm to the nuclear compartment was evident in all normal endometrial cells exposed to E2, DES or OH-TX for two hours. While cells from the endometrial cancer 'S', like the normal cells, translocated IF to the nucleus, cells of another cancer ('KLE') failed to translocate when exposed to E2 or OH-TX. Partial translocation was evident in 'KLE' cells exposed to DES. In MCF-7 cells grown in the absence of E2, IF was exclusively cytoplasmic. When these cells were exposed to the hormones, 50% showed a complete transfer of IF to the nucleus; in 40% a delayed response was evident; 10% failed to translocate. The results revealed the suitability of anti-ER antibodies for investigating the intracellular dynamics of ER in target cells responding to estrogens or antiestrogens.

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