Chronic inflammation is associated with increased erythrocyte adhesiveness/aggregation. This might have deleterious effects on the microcirculatory flow and tissue oxygenation. We aimed to determine the degree of erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with inflammatory bowel disease (IBD). Fifty-two patients (24 women and 28 men) with ulcerative colitis (UC) at a mean age of 44.0+/-16.8 years and 96 patients (44 women and 52 men) with Crohn's disease (CD) at a mean age of 38.0+/-15.5 years, with various degrees of disease activity, were matched to normal controls. A simple slide test and image analysis were used to determine the degree of erythrocyte adhesiveness/aggregation. CD activity index (CDAI) was determined in patients with CD, while clinical colitis activity index was applied for patients with UC. A significant (P < 0.0005) increment in the degree of erythrocyte adhesiveness/aggregation was noted in both groups of IBD patients compared with matched control groups. This increment was evident even in individuals with a low index of disease activity and during remission. The highly significant correlation with the concentrations of fibrinogen suggests that the degree of erythrocyte adhesiveness/aggregation is an inflammation-related phenomenon. An enhanced state of erythrocyte adhesiveness/aggregation was noted in the peripheral blood of patients with IBD. This might have a deleterious effect on intestinal microcirculatory flow and tissue oxygenation.