The purpose of this study is to see if infliximab is safe and effective in treating GCA. Currently, the only treatment for GCA is prednisone. GCA is a long lasting inflammatory disease. The cause is unknown. It may affect all the arteries, but it focuses on the big vessels such as those around the heart, the vessels in the neck and head, and their major branches. It can lead to vision loss, blindness, stroke, stenosis (narrowing of blood vessels) and aneurysms (a weakening in the lining of the blood vessel wall, which may eventually lead to rupture of the blood vessel). The damage to the arteries is caused by an immune response. A naturally occurring substance in the immune system called "tumor necrosis factor alpha" (TNFa) plays a significant role in this immune response against the blood vessels. This response is thought to cause the long-lasting inflammation (irritation and swelling of the vessels). By blocking the effect of TNFa we think that we may reduce the signs and symptoms associated with GCA. This trial will study patients who are stable on prednisone treatment by evaluating whether infliximab can control their symptoms as the dose of prednisone is reduced. Patients will receive infusions of either 5mg/kg of infliximab or placebo at weeks 0, 2, 6, 14, 22, 30, 38, and 46. Safety evaluations will be performed at specified intervals throughout the study and will consist of laboratory tests, vital signs (such as blood pressure), physical examinations and the occurrence and severity of adverse events as well as other study specific procedures. Patients will receive receive infusions of either 5mg/kg infliximab or placebo infusions at weeks 0, 2, 6, 14, 22, 30, 38, and 46.