Active ulcerative colitis (UC) is associated with elevated granulocytes and monocytes/macrophages (GM) which show activation behavior and increased survival time. Further, fecal calprotectin (a stable neutrophil protein) level parallels intestinal inflammation and can predict UC relapse. Since GM are major sources of inflammatory cytokines and chemokines, they are suspected to have roles in the initiation and perpetuation of UC. Our objective was to investigated relationships between peripheral blood (PB) neutrophils, calprotectin, and UC disease activity. Full PB and calprotectin were determined in 69 healthy controls and 31 patients with UC, then 7 randomly selected patients received GM adsorptive apheresis (GMA) with Adacolumn, 10 sessions of 60-min duration each. Patients with UC had higher neutrophil counts (P < 0.001), but lower lymphocyte counts (P < 0.001) compared with controls. Further, fecal calprotectin levels showed a correlation with UC clinical activity index (CAI; P < 0.001) and mucosal inflammation (P < 0.001). Following GMA, there were falls in neutrophils (P < 0.02), CAI (P < 0.02) and calprotectin (P < 0.02). In conclusion, GM appear to contribute to intestinal inflammation and UC activity and reduction of these cells by GMA should benefit patients with active UC. Further, the correlations among calprotectin, UC activities, and PB neutrophils should serve as the basis for preemptive actions to control this disease.