The tumor tissue produces many factors which modulate the autonomous features specific to tumors (carcinogenesis, angiogenesis, apoptosis etc.) and, from the other hand, determines functional and morphological disorders in the paraneoplasic tissue; this was notified by Bochman. These substances are represented by biological amines and vasoactive peptides, where a special role is attributed to serotonin. Using Ribonuclease Protection Assay (RPA) method we analyzed the level of mRNA for Tph-1 in tumors from 164 patients with endometrial cancer and in 54 non-cancer endometrial specimens. We identified that in more than 70% of endometrial cancer the level of mRNA for Tph-1 was increased 2-100 folds in comparison with non-cancer endometrium. Additional, the levels of mRNA for Tph-1 in non-cancer endometrium and subjacent miometrial layer from cancer and non-cancer patterns were comparable, thus, we demonstrated the direct implication of local factors of serotoninergic system in the evolution of endometrial cancer.