Patients must have stable psoriasis vulgaris, which covers at least 10% of their bodies, for at least six months. Patients can not have not been treated with narrowband UVB in the past, although other light therapies are acceptable (i.e. broadband UVB and PUVA). Patients are not allowed to receive other therapies for their psoriasis, internal and topical, while they are participating in the study. Patients may continue using non-medicated moisturizer.