Act as medical supervisor and coordinating center for a five-year additional follow-up study of approximately 1,300 patients who received oral psoralen photochemotherapy and were followed by the incumbent contractor to determine the short- and long-term effects of this new psoriasis treatment. The Contractor will serve as a coordinating center for sixteen or fewer subcontractors and will be responsible for adherence by the subcontractors to the objectives and work scope of the five-year study.