Zearalenone (ZEA), a nonsteroidal mycotoxin with estrogen-like activity, is synthesized by molds (Fusarium) commonly contaminating poorly stored agricultural products and foodstuffs. Human ER binds ZEA and this is probable mechanism of its action, although their influence on target tissues seems to be weaker (80-160 less active) comparing to E2. Zea has been observed to possess tumor-promoting activity similar to that of estrogens and hypothetically can inducing proliferation and carcinogenesis in estrogen-dependent tissues. Nowadays, the questions are, if ZEA is present in human endometrium and whether concentrations of this mycoestrogen is associated with endometrial cell proliferation. Endometrial tissues specimens were collected from 49 women (endometrial adenocarcinoma n = 27, endometrial hyperplasia n = 11, normal proliferative endometrium n = 11). Mean tissue zearalenone concentration in 3 endometrial hyperplasia and 22 adenocarcinoma samples was 47.8 +/- +/- 6.48 and 167 +/- +/- 17.69 ng/ml respectively in contrary to normal endometrium where tissue mycoestrogen concentration was not detectable. In 8 cases of hyperplastic and 5 cases of neoplastic endometrial tissue specimens ZEA was not observed. Our findings confirm the presence of ZEA in hyperplastic and neoplastic endometrium and therefore this substance might be of importance in carcinogenesis.