Hypothesis/aims of study. Endometriosis is one of the most pressing problems of gynecology. Clarifying the expression of the estrogen receptor (ESR1) and the progesterone receptor (PGR) genes and polymorphisms in the aromatase (CYP19A1) gene in endometriosis will expand the understanding of the pathogenesis of the disease and the causes of resistance to its therapy. The objective of this study was to conduct a comparative analysis of mRNA expression of PGR, ESR1 and CYP19A1 genes in paired samples of the eutopic endometrium and peritoneal endometrioid lesions in order to search for predictive markers of response to hormonal therapy. In the future, this may allow personalizing the selection of hormonal preparations for the treatment of endometriosis. Study design, materials and methods. Reverse transcription real-time PCR made it possible to evaluate CYP19A1, PGR and ESR1 gene expression levels in studied tissue samples from 22 patien