AIM: To evaluate peripheral blood lymphocyte subsets in patients with acute pancreatitis (AP).METHODS: Twenty patients with mild AP (M-AP) and 15 with severe AP (S-AP) were included in our study. Pe-ripheral blood lymphocytes were examined at d 1-3, 5, 10 and 30 by means of ? ow cytometry. RESULTS: A signifi cant depletion of circulating lympho-cytes was found in AP. In the early AP, the magnitude of depletion was similar for T- and B- lymphocytes. In the late course of S-AP, B-lymphocytes were much more depleted than T-lymphocytes. At d 10, strong shift in the CD7+/CD19+ ratio implicating predominance of T- over B-lymphocytes in S-AP was found. Among T-lym-phocytes, the signifi cant depletion of the CD4+ popula-tion was observed in M-AP and S-AP, while CD8+ cells were in the normal range. Lymphocytes were found to strongly express activation markers: CD69, CD25, CD28, CD38 and CD122. Serum interleukin-2 (IL-2), IL-4, IL-5, IL-10, interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) levels were signifi cantly increased in both forms of AP. The magnitude of elevation of cytokines known to be produced by Th2 was much higher than cytokines produced by Th1 cells.CONCLUSION: AP in humans is characterized by significant reduction of peripheral blood T- and B-lymphocytes. AIM: To evaluate peripheral blood lymphocyte subsets in patients with acute pancreatitis (AP). METHODS: Twenty patients with mild AP (M-AP) and 15 with severe AP (S-AP) were included in our study. Pe-ripheral blood lymphocytes were examined at d 1-3, 5, 10 and 30 by means of? ow cytometry. RESULTS: A signifi cant depletion of circulating lympho-cytes was found in AP. In the early AP, the magnitude of depletion was similar for T- In the late course of S-AP, B-lymphocytes were much more depleted than T-lymphocytes. At d 10, strong shift in the CD7 + / CD19 + ratio implicating predominance of T- over B-lymphocytes in S- AP was found. Among T-lym-phocytes, the signifi cant depletion of the CD4 + popula tion was observed in M-AP and S-AP, while CD8 + cells were in the normal range. Lymphocytes were found to strongly express activation markers: Serum interleukin-2 (IL-2), IL-4, IL-5, IL-10, interferon-γ (IFN- γ) and tumor necrosis factor-α The magnitude of elevation of cytokines known to be produced by Th2 was much higher than cytokines produced by Th1 cells. CONCLUSION: AP in humans is characterized by significant reduction of peripheral blood T- and B-lymphocytes.