This study will evaluate the effectiveness and safety of the experimental compound OP2000 (deligoparin) in patients with active ulcerative colitis. Patients eligible for this study will have received (and will continue to receive) stable doses of aminosalicylates (oral, enema and/or suppository), if tolerated. OP2000 is an ultra low molecular weight heparin with anticoagulant (blood thinning) and anti-inflammatory actions that may be of benefit for the treatment of ulcerative colitis.