BACKGROUND: Infliximab, a chimeric monoclonal antibody directed against tumor necrosis factor α, is an established treatment for Crohn‘s disease but not ulcerative colitis. METHODS: Two randomized, double-blind, placebo-controlled studies -the Active Ulcerative Colitis Trials 1 and 2 (ACT 1 and ACT 2, respectively) -evaluated the efficacy of infliximab for induction and maintenance therapy in adults with ulcerative colitis. In each study, 364 patients with moderate-to-severe active ulcerative colitis despite treatment with concurrent medications received placebo or infliximab (5 mg or 10 mg per kilogram of body weight) intravenously at weeks 0, 2, and 6 and then every eight weeks through week 46 (in ACT 1) or week 22 (in ACT 2). Patients were followed for 54 weeks in ACT 1 and 30 weeks in ACT 2. RESULTS: In ACT 1, 69 percent of patients who received 5 mg of infliximab and 61 percent of those who received 10 mg had a clinical response at week 8, as compared with 37 percent of those who received placebo (P < 0.001 for both comparisons with placebo). A response was defined as a decrease in the Mayo score of at least 3 points and at least 30 percent, with an accompanying decrease in the subscore for rectal bleeding of at least 1 point or an absolute rectal-bleeding subscore of 0 or 1. In ACT 2, 64 percent of patients who received 5 mg of infliximab and 69 percent of those who received 10 mg had a clinical response at week 8, as compared with 29 percent of those who received placebo (P < 0.001 for both comparisons with placebo). In both studies, patients who received infliximab were more likely to have a clinical response at week 30 (P ≤0.002 for all comparisons). In ACT 1, more patients who received 5 mg or 10 mg of inflix imab had a clinical response at week 54 (45 percent and 44 percent, respectively) than did those who received placebo (20 percent, P<0.001 for both comparisons) . CONCLUSIONS: Patients with moderate-to-severe active ulcerative colitis treated with infliximab at weeks 0, 2, and 6 and every eight weeks thereafter were more likely to have a clinical response at weeks 8, 30, and 54 than were those receiving placebo. BACKGROUND: Infliximab, a chimeric monoclonal antibody directed against tumor necrosis factor α, is established treatment for Crohn’s disease but not ulcerative colitis. METHODS: Two randomized, double-blind, placebo-controlled studies-the Active Ulcerative Colitis Trials 1 and 2 (ACT 1 and ACT 2, respectively) -evaluated the efficacy of infliximab for induction and maintenance therapy in adults with ulcerative colitis. In each study, 364 patients with moderate-to-severe active ulcerative colitis despite treatment with concurrent medications received placebo or infliximab (5 mg or 10 mg per kilogram of body weight) intravenously at weeks 0, 2, and 6 and then every eight weeks through week 46 (in ACT 1) or week 22 (in ACT 2). Patients were followed for 54 weeks in ACT 1 and 30 weeks in ACT 2. RESULTS: In ACT 1, 69 percent of patients who received 5 mg of infliximab and 61 percent of those who who received 10 mg had a clinical response at week 8, as compared with 37 percent of those w ho received placebo (P <0.001 for both comparisons with placebo). A response was defined as a decrease in the Mayo score of at least 3 points and at least 30 percent, with an accompanying decrease in the subscore for rectal bleeding of at least 1 point or an absolute rectal-bleeding subscore of 0 or 1. In ACT 2, 64 percent of patients who received 5 mg of infliximab and 69 percent of those who who received 10 mg had a clinical response at week 8, as compared with 29 percent of Those who received placebo (P <0.001 for both comparisons with placebo). In both studies, patients who received infliximab were more likely to have a clinical response at week 30 (P ≤ 0.002 for all comparisons). In ACT 1, more patients who received 5 mg or 10 mg of inflix imab had a clinical response at week 54 (45 percent and 44 percent respectively) than did those who who received placebo (20 percent, P <0.001 for both comparisons). CONCLUSIONS: Patients with moderate-to -severe active ulcerative colitis treated wit h infliximab at weeks 0, 2, and 6 and every eight weeks thereafter were more likely to have a clinical response at weeks 8, 30, and 54 than those receiving placebo.