Many patients with ulcerative colitis are refractory towards conventional therapies, highlighting a need for treatments with novel mechanisms of action. Promising targets include cell adhesion molecules such as MADCAM1 that mediate the migration of lymphocytes into sites of inflammation in the gut. In a phase II, randomized, placebo-controlled trial, the efficacy and safety of PF-00547659 — a human monoclonal antibody to MADCAM1 — was assessed in moderate to severe ulcerative colitis. Patients (n = 357) from 105 centres in 21 countries were randomized to receive placebo or one of four doses of PF-00547659 every 4 weeks. The primary endpoint was induction of clinical and endoscopic remission by week 12. In three of the four treatment groups (7.5 mg, 22.5 mg and 75 mg), remission rates were significantly greater than placebo, with the greatest clinical effects seen with doses of 22.5 mg and 75 mg. No safety or tolerance concerns were reported