To elucidate the molecular mechanisms involved in the therapeutic effects of granulocyte/monocyte adsorption apheresis, changes were investigated in the cytokine responses of peripheral blood mononuclear cells (PBMC) before and after granulocyte/monocyte adsorptive apheresis in ulcerative colitis (UC) patients. Four patients with active UC were enrolled. All patients responded to granulocyte/monocyte adsorptive apheresis. A total of 20 sessions of four patients were analyzed. Peripheral blood mononuclear cells were isolated from peripheral venous blood within 5 min before and after each session of granulocyte/monocyte adsorptive apheresis. The cells were stimulated with interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha for 24 h, and the secreted IL-8 and IL-6 levels were determined by enzyme-linked immunosorbent assay (ELISA). IL-1beta-induced IL-8 and IL-6 secretion was significantly decreased after granulocyte/monocyte adsorptive apheresis. TNF-alpha-induced IL-8 secretion was also significantly decreased after apheresis, but there was no significant difference in TNF-alpha-induced IL-6 secretion (P = 0.052). In conclusion, granulocyte/monocyte adsorptive apheresis down-regulates the IL-1beta- and TNF-alpha-induced inflammatory responses in PBMC. The induction of hyporesponsiveness to pro-inflammatory cytokines may be an important factor mediating the clinical effects of granulocyte/macrophage adsorptive apheresis in UC patients.