The aim of this investigation was to study the involvement of eosinophil and neutrophil granulocytes in different stages of Crohn's disease (CD) and ulcerative colitis (UC). Biopsy samples were taken from the right flexure of the colon and from the rectum in patients with active (n=12) and inactive colonic CD (n=7), patients with active (n=33) and inactive UC (n=24), and from control subjects (n=11). Cell suspensions from biopsies and blood were analyzed by flow cytometry with regards to activation markers and viability. Immunohistochemistry was used to evaluate cell number and degranulation. Blood eosinophils were cultured with Th1 and Th2 cytokines, and the expression of activity markers was assessed by flow cytometry. Eosinophil number, viability, and activity were increased during active CD and UC compared with controls. The activity, assessed as CD44 expression, tended to diminish during inactive CD but was increased further in quiescent UC. Neutrophil number and activity were increased only during inflammation in both diseases. Culture of blood eosinophils with IL-5 and IL-13 caused increased CD44 expression, whereas IL-5 and IFN-gamma induced elevated CD69 expression. We observed different patterns of eosinophil activation in CD and UC, with the highest CD44 expression during quiescent UC. Our in vitro experiments with recombinant cytokines suggest that the diverse mechanisms of eosinophil activation in CD and UC are a result of different cytokine milieus (Th1 vs. Th2). In contrast, neutrophil activation reflects the disease activity in CD and UC, irrespective of Th cell skewing.