In order to assess possible ovarian cell potential for interaction with tamoxifen, thus demonstrating possible effects of this agent on the development of ovarian pathologies through growth stimulation and cell proliferation, we measured estrogen receptors (ER) and progesterone receptors (PR) by immunohistochemical method in 16 benign ovarian tumors removed from 11 postmenopausal breast cancer patients treated with tamoxifen (study group). The results were compared with those measured in 7 similar ovarian tumors obtained from 5 similar patients without tamoxifen treatment (control group I), and in 9 similar tumors removed from 9 age-matched postmenopausal women (control group II). There were no significant differences with regard to ER or PR expression between the study group and control group I and II (ER = 18.75, 0.0 and 11%, respectively; PR = 43.75, 28.5 and 44%, respectively; p = NS). There were also no significant statistical differences between the three groups when subdividing the ovarian pathologies according to different histological types. From the results obtained in this study, it seems that tamoxifen probably does not have any direct influence on the ovaries of menopausal breast cancer patients.