Crohn's disease has frequently been associated with coagulation abnormalities, causing intravascular deposition of fibrin and local infarction which can subsequently compromise the gut mucosa. Also, arterial and venous thromboembolic complications of larger vessels appear to be associated with Crohn's disease. Coagulation activation in patients with Crohn's disease could be a result of increased serum and tissue levels of cytokines, as reported. We prospectively studied parameters of coagulation and fibrinolysis in 10 patients with active Crohn's disease, who were subsequently treated with a monoclonal anti-tumor necrosis factor-alpha (TNF) antibody. Ten consecutive patients with active Crohn's disease (CDAI > 150), not responding to a daily dose of at least 20 mg prednisolone, received a single infusion of human/mouse chimeric anti-TNF antibody cA2. All evaluable patients attained complete clinical and endoscopic