INTRODUCTIONLow-molecular-weight heparins are preparations made by partial hydrolysis or enzymatic degradation of unfractionated heparin. 1, 2 They are considered to be as effective an anticoagulant as unfractionated heparin and to have better pharmacodynamic and pharmacokinetic pro®les. Clinical data suggest that lowmolecular-weight heparins are safer than unfractionated heparin. 3 It was recently found that, like unfractionated heparin, low-molecular-weight heparins possess anti-in¯ammatory properties, independent of their anticoagulant properties. 4,5 The anti-in¯amma-tory effects of low-molecular-weight heparins were demonstrated in both animal models of in¯ammation and in human diseases. Low-molecular-weight heparin signi®cantly decreased hepatic damage in immunemediated concanavalin-A hepatitis in mice. 6 It reduced SUMMARY Background and aims: The anticoagulants, unfractionated heparin and low-molecular-weight heparin, demonstrated anti-in¯ammatory effects in animal models and in humans. Because of its dual effects, high-dose heparin was proposed as a therapeutic modality for ulcerative colitis. We investigated whether a low dose of low-molecular-weight heparinÐenoxaparin (Clexane, Rho Ãne-Poulenc Rorer, France)Ðameliorates the in¯am-matory response in two models of experimental colitis. Methods: Colitis was induced in rats by intrarectal administration of dinitrobenzene sulphonic acid. Enoxaparin (40, 80 and 200 lg/kg) or unfractionated heparin (100, 200 and 400 U/kg) were administered subcutaneously immediately after the induction of damage. Enoxaparin, 80 lg/kg, was also administered after induction of colitis by intrarectal administration of