Inclusion Criteria:

• Subjects must have met all inclusion/exclusion criteria in Study P04271.
• Subjects must have been originally randomized to infliximab in Study P04271.
• Subjects must have completed the full 26 weeks of Study P04271.
• Subjects must have remained on infliximab for the full 22 weeks of treatment in Study P04271.
• Subjects must have achieved an improvement in Psoriasis Area and Severity Index (PASI) score >=75% from Baseline of Study P04271 to Week 26 of Study P04271.
• Subjects must agree to avoid prolonged sun exposure and avoid use of tanning booths or other ultraviolet light sources during the study.

• Subjects are considered eligible according to the following tuberculosis (TB) criteria:

  • Have no signs or symptoms suggestive of active TB upon medical history and/or physical examination;
  • Have had no recent close contact with a person with active TB or, if there has been such contact, will be referred to a physician specializing in TB to undergo additional evaluation and, if warranted, receive appropriate treatment for latent TB prior to or simultaneously with the first administration of study medication.

• Subjects' Baseline (Visit 1) clinical laboratory tests (CBC, blood chemistry, and urinalysis) must be within the following parameters:

  • Hemoglobin >=10 g/dL
  • White blood cells >=3.5 x 10^9/L
  • Neutrophils >=1.5 x 10^9/L
  • Platelets >=100 x 10^9/L
  • Serum creatinine <1.5 mg/dL (or <133 <mol/L)
  • Aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and gamma-glutamyltransferase levels as outlined in Protocol P04563.
  • Total bilirubin <2 x upper limit of normal [Note: If Baseline laboratory tests are not yet available, then the previous laboratory tests from Week 22 of the parent study (Study P04271) should be used for enrollment. When the Baseline laboratory tests become available, the investigator must apply the above parameters to determine a subject's eligibility.]
• Subjects must be free of any clinically significant disease (other than plaque-type psoriasis or psoriatic arthritis) that would interfere with the study evaluations.
• Subjects must be willing to give written informed consent and be able to adhere to dose and visit schedules.
• Women of childbearing potential and all men must be using adequate birth control measures (eg, abstinence, oral contraceptives, intrauterine device, barrier method with spermicide, or surgical sterilization) and must continue using such measures until 6 months after receiving the last infusion of study medication.
• Female subjects of childbearing potential must have a negative urine pregnancy test at Baseline.

Exclusion Criteria:

• Subjects who have any significant ongoing adverse events (AEs) or AEs from P04271 that would prohibit further treatment with infliximab at the time of entry.
• Subjects originally randomized to methotrexate or subjects who received methotrexate at any time during their participation in Study P04271.
• Subjects who have non-plaque forms of psoriasis (eg, erythrodermic, guttate, or pustular).
• Subjects who have current drug-induced psoriasis (eg, a new onset of psoriasis or an exacerbation of psoriasis from beta blockers, calcium channel blockers, or lithium).
• Female subjects who are pregnant, nursing, and both men and women who are planning pregnancy during the study period or during the 6 months after receiving of the last infusion of study medication.
• Subjects who are in a situation or have any condition that, in the opinion of the investigator, may interfere with optimal participation in the study.
• Subjects who are staff personnel directly involved with this study.
• Subjects who are family members of the investigational study staff.