Estrogen target genes play essential role among pathogenetic and prognostic factors of endometrial adenocarcinoma; and among them estrogen receptor genes. Although prevailing estrogen receptor type is ER-alpha in endometrium, transduction of signal carried by estrogens can be also mediate by ER-beta, which biological meaning relies on modulation of ER-alpha transcriptional activity. There is hypothesized that ER-beta can keep under control mitogenic activity mediating by ER-alpha. The aim of the study was qualitative and quantitative analysis of wtER-beta and ER-beta/delta 5-6, ER-beta/delta 6 isoforms in endometrial adenocarcinoma. Material used in the study included specimens obtained from 27 female: group I--normal endometrium (n = 12), group II--endometrial adenocarcinoma (n = 15). RNA was extracted from the analyzed material using phenol-chloroform method by Total RNA Prep Plus. Qualitative analysis was performed basing on RT-PCR reaction and polyacrylamide gel electrophoreses. For all RNA extracts of the samples examined RT-PCR was performed with a sequence detector ABIPRISMTM7700--Perkin-Elmer Applied Biosystems (RT: 600 C-30 min; PCR: 950 C-5 min, 40 cycles: 950 C-30s, 600 C-1 min, and 720 C-10 min) in order to determine the number of RNA copies (which corresponds to the number of cDNA copies) for wtER-beta and ER-beta/delta 5-6 and ER-beta/delta 6. Specificity of QRT-PCR reaction was determined by delimitation of melting temperature of all examined amplimers (ABI PRISM7000, Qu-antiTect SYBR Green RT-PCR Kit) and by sequence analysis using ABI PRISM377 DNA Sequencer. Wild-type of estrogen receptor beta and ER-beta/delta 5-6, ER-beta/delta 6 isoforms--coming into alternative splicing of mRNA, presented both, in proliferative endometrium and endometrial adenocarcinoma. Copy number of wtER-beta mRNA was significantly (p < 0.05, Mann-Whitney U test) lower in comparison with proliferative endometrium and correlated with decrease of ER-beta/delta 6 mRNA copy number (r = 0.85; p < 0.05). Preliminary results confirming decrease of wtER-beta, ER-beta/delta 5/6 and ER-beta/delta 6 mRNA copy number in endometrial adenocarcinoma can show their relationship with high risk of carcinogenesis.