• The primary outcome measure is corticosteriod free remission at week 26. [ Time Frame: Week 26 ] [ Designated as safety issue: No ]
  

• The secondary outcome measure is mucosal healing at Week 26. [ Time Frame: Mucosal healing - at Week 26; Remission without steroids for 3 weeks - at Week 50; Clinical Response - through Week 50; Remission - through Week 50; QOL - through Week 50; Corticosteroid dose - through Week 50; Safety - through Week 54. ] [ Designated as safety issue: No ]
  

Crohn's disease is characterized by inflammation (the changes that happen when tissues in the body are injured) and ulceration (open sores) of the intestines. It is generally treated with medications that decrease inflammation, and reduce diarrhea, abdominal pain and other symptoms of Crohn's disease. In addition, Crohn's disease can be treated with medications that suppress the immune system (the body system involved in inflammation and infections) or with surgery. This study will investigate the effectiveness of REMICADE® (infliximab) and Imuran® (the generic name is azathioprine) in the treatment of patients with moderate-to-severe Crohn's disease. REMICADE® is currently approved by the FDA for the treatment of both Crohn's disease and rheumatoid arthritis. Azathioprine, which is an investigational drug, has not been approved by the FDA for the treatment of Crohn's disease, but it is a well-established therapy that has been used for many years to treat Crohn's disease. This study seeks to determine whether REMICADE®, azathioprine, or the combination of both drugs would be the most appropriate treatment for Crohn's disease patients who have not responded well to certain drugs called 5-ASA drugs (e.g. Asacol, Pentasa, sulfasalazine) and/or require frequent treatment with corticosteroids. This research study will involve approximately 500 patients. Patients may participate in the main study for up to 34 weeks (approximately 8 months). During the main study, patients will be asked to visit the study center for 10 visits. If patients enroll into the extension of the study, the total time for participation may be up to 54 weeks (approximately 13 months). Patients enrolled in the Study Extension will be asked to visit the study center for an additional 5 visits.

Patients will be assigned to one of three treatment groups (either infliximab plus placebo capsules, infliximab plus azathioprine, or azathioprine plus placebo infusions - there is no possibility of being assigned to placebo only in this trial - patients will receive one or both of these medications) at the beginning of the study. Oral medication will be taken daily. There are 5 infusion (which will be either infliximab or placebo) visits during the main study.