【Abstractt】 Objective To evaluate the effects of high volume hemofiltration (HVHF) on cellular immunity in patients with multiple organ dysfunction syndrome (MODS). Methods Fourteen MODS patients subjected to HVHF were enrolled in this study. Five mililiters of blood sample were collected from these patients before HVHF and after 1, 3 and 5 days of HVHF to count blood monocytes and to analyze lymphocyte subsets including CD3+, CD4+, CD8+ and the expression of HLA-DR on monocytes by flow cytometry. Results In the 14 patients, 9 patients survived and 5 died. In the survival patients after HVHF, the ratios of CD3+ and CD4+ and CD4+/CD8+ increased; CD3+ ratio increased significantly (P＜0.05) at the 5th day after HVHF, CD4+ and D4+/CD8+ ratios increased significantly (P＜0.05) at the 3rd and 5th days after HVHF, and CD8+ ratio decreased gradually and significantly (P＜0.05) at the 3rd and 5th days after HVHF. Additionally, blood monocytes count and the ratio of positive HLA-DR on blood monocytes increased at the 1st day after HVHF (P＜0.05) and significantly increased at the 3rd and 5th days after HVHF (P＜0.01). In the death patients after the treatment, however, no remarkable changes were found in the ratios of lymphocyte subsets, blood monocytes count and the ratio of positive HLA-DR on blood monocytes (P＞0.05). Conclusion HVHF may regulate the ratio of lymphocyte subsets, increase blood monocyte count, improve the antigen presenting function, and alleviate the immunosuppressive status in MODS patients.