Endometrium is a specialized organ in which phenomena controlling the level of cell proliferation and apoptosis are marked. The aim of our study was to determine the presence of proteins involved in apoptosis and proliferation: RCAS1, MT and the number of CD56- positive cells and their activity to elucidate their possible role in the development of adenocarcinoma and endometriosis. Materials and methods. MT, RCAS1, CD56- positivity and CD69 expression were assessed in 55 tissue samples by Western blot and immunohistochemistry methods. Results. We found that endometrium during secretory menstrual cycle phase is characterized by significantly higher RCAS1 and higher MT expression than in proliferative phase. The number of CD56- positive cells and the CD69 antigen expression was significantly increased. Endometrial adenocarcinoma was characterized by significantly increased RCAS1 expression, while MT expression was comparable to the level found in the secretory phase. The number of CD56- positive cells was significantly decreased and their activity was comparable to the level found in the secretory phase. Endometriosis was accompanied by significantly lower RCAS1 and MT expressions, with lower number of CD- 56 positive cells and lower expression of CD69 antigen in comparison to the secretory phase. Conclusions. The ability of endometrium to determine cytotoxic activity (RCAS1 expression changes) and high protection against DNA damage (MT expression) with concomitant changes in the number of immune cells and their activity, observed in normal endometrium during the menstrual cycle phases sems to be fundamental for pathological features of endometrial adenocarcinoma and endometriosis. The aim of our study was to determine the presence of proteins involved in apoptosis and proliferation: RCAS1, MT and the number of CD56-positive cells and their activity to elucidate their possible role in the development of adenocarcinoma and endometriosis. Materials and methods. MT, RCAS1, CD56-positivity and CD69 expression were evaluated in 55 tissue samples by Western blot and immunohistochemistry methods. Results. We found that endometrium during secretory menstrual The number of CD56-positive cells and the CD69 antigen expression was significantly increased. Endometrial adenocarcinoma was characterized by significantly higher RCAS1 and higher MT expression than in proliferative phase. level found in the secretory phase. The number of CD56- positive cells was significantly decreased and their activity was comparable to the level found in the secretory phase. Endometriosis was accompanied by significantly lower RCAS1 and MT expressions, with lower number of CD-56 positive cells and lower expression of CD69 antigen in comparison to the secretory phase. Conclusions. The ability of endometrium to determine cytotoxic activity (RCAS1 expression changes) and high protection against DNA damage (MT expression) with concomitant changes in the number of immune cells and their activity, observed in normal endometrium during the menstrual cycle phases sems to be fundamental for pathological features of endometrial adenocarcinoma and endometriosis.