 Inclusion Criteria: - Chronic plaque psoriasis eligible for systemic therapy and NB-UVB in the opinion of the investigator - Psoriasis Activity and Severity Index PASI greater than or equal to 15 and at least 25 of individual plaques must be considered severe - Patients must have body surface area BSA involvement of greater than or equal to 5 - Before any study-specific procedure, subject must sign and date the appropriate written informed consent - Negative urine pregnancy test within 7 days before the first dose of study drug in all women except those surgically sterile or at least 5 years postmenopausal - Sexually active subjects of childbearing potential must agree to use medically acceptable form of contraception during screening and throughout the study 