Ulcerative Colitis (UC) is a disorder involving the lining of the colon. A substance called "tumor necrosis factor" (TNF) naturally occurs in the body. TNF is thought to play an important role in the development of ulcerative colitis by causing some of the damage that is seen in the colon. "Antibodies" are normally made in the body and help fight off infection. Infliximab is an antibody that is made in a scientific laboratory, using parts of both mouse and human antibodies. It has been designed to attach to TNF, making it difficult for TNF to do any damage. This study will be done at centers in North America and Europe. Each child will first have a clinic visit (screening visit) to have some tests done to make sure the child is the type of patient who should be in this study. At the 2nd visit (week 0), the child will have the first treatment with infliximab. All children in the study will receive 5 mg/kg infliximab 3 times (at weeks 0, 2 and 6) over the first 6 weeks of the study. If the child's symptoms do not improve by the 8th week, the child will receive no further infusions, but will return for safety evaluations. If the child's symptoms do improve, the child will be randomly assigned (like the flip of a coin) to either 5 mg/kg infliximab every 8 weeks through week 46 or 5 mg/kg infliximab every 12 weeks through week 42. If the child gets worse after being randomly assigned, the amount of infliximab may be increased or the infliximab may be given more frequently. A final infusion will be given at either week 42 or week 46. There will be a safety evaluation at week 54 and a visit at week 62 to get a blood sample. Patients will receive 5 mg/kg of infliximab at weeks 0, 2 and 6 and then 5mg/kg infliximab either every 8 weeks or 12 weeks until weeks 42 or 46. Infliximab is given as an intravenous infusion over 2 hours.
