Estrogen receptor (ER)-beta may play a significant role in estrogen action in several human tissues. Estrogen receptor beta may act as a transdominant repressor of ER alpha transcriptional activity trough heterodimers form. Estrogen receptor messenger RNA (mRNA) variants also may be involved in various diseases, including endometrial cancer. The absence of estrogen receptors has often correlated with poor prognosis of endometrial tumors. The objective of the study was to determine the number of mRNA ER beta delta 6 and (wtER beta) in 1 microgram total RNA obtained from tissues of normal, hyperplastic endometrium, and endometrial adenocarcinoma. This study was designed to evaluate possible differences in the ER beta delta 6 and wtER beta messenger RNA (mRNA) level in the normal, hyperplastic endometrium, and endometrial endometrioid adenocarcinoma (G1, G2 morphological degree). Adenocarcinoma showed significantly lower ER beta delta 6 mRNA level than proliferative (p = 0.032) and secretory (p = 0.01) endometrium. A decrease of mRNA wtER beta in endometrial adenocarcinoma (p = 0.006) also was observed.