The purpose of this clinical research study is to determine the safety, pharmacokinetics, immunogenicity in humans, the recovery time required from the biologic effects and the optimal biologic dose range of BMS188667 (CTLA4Ig)

Inclusion Criteria:

• Men or women who received adequate counseling and were judged reliabel in their use of contraceptive measures.
• Diagnosis and documentation of stable psoriasis vulgaris of at least 6 months duration.
• Psoriasis vulgaris total body surface area involvement between 10% and 49% (Overall Disease Severity Score [ODSS]of 4-7 inclusive).
• Failure of toxicity or inefficacy of at least one standard antipsoriatic therapy including topical treatment, etretinate, phototherapy, or methotrexate.

Exclusion Criteria:

• Treatment with: a) Retinoids within 2 years, b) cyclosporin A, systemic corticosteroids, methotrexate, or an investigational agent within 16 weeks, c) any phototherapy or photochemotherapy within 4 weeks d) any topical psoriasis treatment other than emollients within 2 weeks prior to enrollment.
• No clinical response to a prior adequate therapeutic trial of cyclosporin A
• Prolonged exposure to the sun within 4 weeks prior to the first dose.
• Guttate, erythrodermic, or pustular psoriasis.
• Spontaneously improving or rapidly deteriorating psoriasis vulgaris.