The purpose of the study is to evaluate the safety and effectiveness of scheduled and as needed treatment of psoriasis with infliximab. Infliximab (Remicade) targets specific proteins in the body's immune system to help control the development of inflammation to help reduce painful disease.

This is a phase III, multicenter, randomized (patients are assigned different treatments based on chance), double-blind (neither the patient nor the physician knows whether drug or placebo is being taken, or at what dosage), placebo-controlled trial evaluating the effectiveness and safety of scheduled and as needed treatment with infliximab in patients with plaque-type psoriasis. This study will also help determine the way to use infliximab in treating patients with psoriasis.

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 infusions of either placebo, 3mg/kg or 5 mg/kg infliximab (Remicade) at weeks 0, 2, 6 14, 18, 22, 26, 30, 34, 38, 42 and 46. Patients receive either 3mg/kg, 5 mg/kg or placebo infusions at week 0, 2, and 6. The 3mg/kg and 5 mg/kg infliximab groups then receive either every 8 week infusions or infusions as needed when their psoriasis is less than 75% improved from baseline. The placebo patients begin infliximab at week 16, 18 and 22 followed by every 8 week infusions.

Inclusion Criteria:

• Patients with diagnosis of plaque-type psoriasis for at least 6 months
• Patients with plaque-type psoriasis covering at least 10% of the body

Exclusion Criteria:

• Patients with nonplaque forms of psoriasis
• Patients who have current drug-induced psoriasis
• Patients who are pregnant, nursing, or planning pregnancy (both men and women) within 18 months of enrollment
• Patients who had any previous treatment with infliximab or any therapeutic agent targeted at reducing tumor necrosis factor