Objectives: Benign prostatic hyperplasia (BPH) and prostatic carcinoma (CaP), following the uroinfections, are the most common diseases in urologic everyday practice. Both entity present “disease of aged male population” and their incidence rise with aging. Past several years, the investigations showed possible role of immune system in the pathogenesis of BPH and CaP, but precise mechanism of their development and progression is still unknown. The purpose of the study was the changes in cell-mediated immunity, especially the frequency of leukocytes subpopulations, expression of cytotoxic mediator perforin, activity of NK cells and expression of cytokines in different immune cells in peripheral blood and prostatic tissue of BPH and CaP patients. Patients, material and methods: Fourthy patients with BPH and 35 patients with CaP were included in the study. Healthy volunteers served as controls. Demographic, clinical and laboratory data (values of prostate specific antigen) were collected and analyzed for each patient. The samples of peripheral blood and prostatic tissue of PBH and CaP patients were collected and sent further immunological investigations. Mononuclear cell for prostatic tissue are separated by enzymatic digestion with 0.1% cllagenase and gradient centriguatlion. Peripheral blood mononuclear cells were obtained after gradient centrifugation. The phenotype of mononuclear cells for prostatic tissue and peripheral blood were analyzed by simultaneous multiple staining of surface antigens using direct immunoflourescency and flow cytometry analyzes. Isolated mononuclear cells were stained simultaneously by monoclonal antibody against surface antigens, specific for different leukocyte populations, and were further permeabilized for intracellular staining of perforin, interleukin IL-4 and IFNγ (interferon gamma). The labeled cells were analyzed by flow cytometry. Cell samples that were scheduled for intracellular cytokine staining were previously stimulated with PMA, ionomycine and monensim which are necessary for cytokine visualization. Immunofluorescency was used for visualization of perforin molecule in the samples of prostatic tissue. CD56+ NK cells were isolated from peripheral blood mononuclear cells by positive magnetic cell separation method. The cytotoxic activity against NK sensitive cell K- 562 cell line of separated CD56+ NK cells of peripheral blood and mononuclear cells isolated form prostatic tissue were tested by 2 hours cytotoxic assay and was analyzed by flow cytometry. Results: Patients with CaP were significantly older and had significantly higher PSA levels than patients with BPH. The frequency of T lymphocytes and its CD3+CD4+CD56- and CD3+CD8+CD56- subpopulations was not significantly different either in the peripheral blood or in the prostatic tissue of patients with BPH and CaP patients. Distribution of CD3+ cells was observed mainly in the epithelium of control prostate tissue and prostate tissue of patients with BPH and CaP patients. The frequency of CD4+CD25+FOXP3+ cells in peripheral blood and prostate tissue was significantly higher in patients with CaP. Although the frequency of NK cells in peripheral blood of patients with BPH, patients with CaP and healthy volunteers did not differ significantly, the frequency of NK cells and their CD3-CD56+dim subpopulation was significantly lower in the prostatic tissue of patients with CaP. Distribution of CD56+ cells was observed in the stroma of prostatic tissue of patients with BPH, patients with CaP and in control prostatic tissue. Marked hyperplasia and increased infiltration of CD56+ cells was observed in the stroma of prostatic tissue of patients with BPH. The frequency of NKT cells was significantly higher in the peripheral blood of patients with BPH than share NKT cells in the peripheral blood of patients with CaP and the control group. The frequency of NKT cells isolated from prostate tissue of patients with BPH and patients with CAP did not differ significantly. Distribution of NKT cells was observed in the epithelium of the control of prostate tissue significantly more than in the epithelium of prostate tissue in patients with BPH and CaP patients. The frequency of B lymphocytes was significantly higher in the peripheral blood of patients with BPH than the frequency of B lymphocytes in the peripheral blood of patients with CaP and the control group. The percentage of B lymphocytes isolated from prostate tissue of patients with BPH and patients with CAP did not differ significantly. The percentage of perforin positive cells was statistically lower in the prostatic tissue of patients with CaP than in patients with BPH. A smaller percentage of perforin was observed in CD3+CD56- T lymphocytes and its CD3+CD4+CD56- and CD3+ CD8+CD56- subpopulations, in NK cells and their CD3-CD56+ subpopulation and inNKT cells isolated from prostate tissue of patients with CaP when compared to patients with BPH. NK cells isolated from peripheral blood of patients with BPH and CaP patients had statistically significant lower cytotoxic activity against K-562 sensitive cell line in comparison to NK cells from peripheral blood of healthy volunteers. Mononuclear cells isolated from prostate tissue of patients with BPH and CaP patients had a small cyotoxic activity against K-562 sensitive cell line. Statistically higher percentage of IFN  + cells was found only in NK cells isolated from patients with BPH, while the percentage of IFN +, and IL-4+ cells did not differ significantly in other lymphocyte subpopulations isolated from prostate tissue of patients with BPH and CaP. A negative correlation was found between the percentages of CD3+CD56- cells in peripheral blood and prostate tissues and PSA in patients with CaP, but not in patients with BPH. We found a positive correlation between the percentage of CD4+CD25+FOXP3+ cells in peripheral blood and prostate tissues and PSA in patients with CaP, but not in patients with BPH. A negative correlation was found between perforin-positive cells, CD3+perforin+, CD56+ perforin+ cells and PSA in prostatic tissue only CaP patients. Conclusion: The results of this study clearly indicate that a small percentage of cells with cytotoxic phenotype, especially NK cells, a small proportion of perforin-positive cells, including T lymphocytes, NK cells and NKT cells, the low cytotoxic activity and the increase of T regulatory cells in patients with BPH, especially in patients with CaP is as a result of local events in prostate tissue and one of the mechanisms involved in the pathogenesis and progression of BPH and CaP. To confirm these results further investigations shoud be preformed.