Fulminating acute ulcerative colitis (UC) is a potentially life threatening medical emergency. Up to 30% of individuals respond poorly to corticosteroids alone and second line medical or surgical therapies are indicated. We describe the successful use of chimeric anti-CD25 therapy in 4 such children poorly responsive to combined therapy with intravenous steroids and calcineurin inhibitors with a pretreatment predictive risk of colectomy of 85-100%. Clinical disease activity scores normalized within 72 hours of anti-CD25 administration and colonic histology provided evidence of mucosal healing within 10-14 days. None required emergency colectomy. Anti-CD25 is efficacious in fulminating UC and randomized placebo controlled trials appear indicated.