Thromboembolic disease is a known complication of ulcerative colitis, but is rarely reported in Crohn's disease. In this study, we have tried to determine if there are indeed coagulation abnormalities associated with these two diseases. Four groups of patients were studies: (1) patients with ulcerative colitis; (2) patients with Crohn's disease; (3) patients with other diseases; (4) healthy control subjects. In both disease groups, platelet counts, factor V, factor VIII, and fibrinogen levels were found to be elevated, while antithrombin III levels were decreased.