Background: Targeting tumour necrosis factor α(TNF-α) has demonstrated effi cacy in Crohn’s disease. Aim: To evaluate CDP571, a humanised antibody to TNF- α, for treating active Crohn’s disease. Patients: A total of 396 patients with moderate to severe Crohn’s disease. Methods: In a 28 week, randomised, double blind, placebo controlled trial, patients received intravenous CDP571 (10 mg/kg) or placebo every eight weeks to week 24. The primary outcome measure was clinic al response (a decrease in the Crohn’s disease activity index (CDAI) to ≥100 p oints or remission (CDAI score ≤150 points)) at week 28. A secondary outcome me asure was clinical response (using the same definition) at week 2. Results: Clin ical response occurred at week 28 in 80/263 (30.4%) CDP571 patients and 31/132 (23.5%) placebo patients (p = 0.102). Clinical response at week 2 occurred in 9 0/263 (34.2%) CDP571 patients and 28/132 (21.2%) placebo patients (p = 0.011). Post hoc exploratory subgroup analysis of 159 patients with baseline C reactive protein (CRP) ≥10 mg/l demonstrated significant differences between CDP571 and placebo in clinical response rates at weeks 2 (CDP571, 50/101 (49.5%); placebo , 9/58 (15.5%); p<0.001) and 28 (CDP571, 29/101 (28.7%); placebo, 7/58 (12.1% ); p = 0.018). Adverse events occurred at similar frequencies in both treatment groups. Conclusions: CDP571 is modestly effective for short but not long term tr eatment of unselected patients with moderate to severe Crohn’s disease. The cli nical relevance of this short term effect is unclear. Post hoc analysis suggests both short and long term efficacy of CDP571 in patients with elevated baseline CRP (≥10 mg/l). CDP571 is well tolerated. Aim: To evaluate CDP571, a humanized antibody to TNF-α, for treating active Crohn’s disease. Patients: A total of 396 patients with moderate to Severe Crohn’s disease. Methods: In a 28 week, randomized, double blind, placebo controlled trial, patients received intravenous CDP 571 (10 mg / kg) or placebo every 8 weeks to week 24. The primary outcome measure was clinic al response in the Crohn’s disease activity index (CDAI) to ≥100 pints or remission (CDAI score ≤ 150 points)) at week 28. A secondary outcome me asure was clinical response (using the same definition) at week 2. Results: Clinical response occurred at week 28 in 80/263 (30.4%) CDP571 patients and 31/132 (23.5%) placebo patients (p = 0.102). Clinical response at week 2 occurred in 9 0/263 (34.2%) CDP571 patients and 28 / 132 (21.2%) placebo patients (p = 0.011). Post hoc exploratory subgroup analysis of 159 patients with baseline C reactive protein (CRP) ≥10 mg / l demonstrated significant differences between CDP571 and placebo in clinical response rates at weeks 2 (CDP571, 50/101 (49.5%); placebo, 9/58 p <0.001) and 28 (CDP571, 29/101 (28.7%); placebo, 7/58 (12.1%); p = 0.018). Adverse events occurred at at least a similar frequency in both treatment groups. Conclusions: CDP571 is modestly effective for short but not long term tr eatment of unselected patients with moderate to severe Crohn’s disease. The cli nical relevance of this short term effect is unclear. Post hoc analysis suggests both short and long term efficacy of CDP571 in patients with elevated baseline CRP (≥10 mg / l). CDP571 is well tolerated.