This chapter discusses the treatment of the most important indications, namely psoriasis, cutaneous T-cell lymphoma, vitiligo, and photodermatoses. Psoralens are tricyclic furocoumarins present in a large number of plants, but there are also some synthetic furocoumarin derivatives. All forms of psoriasis respond to oral PUVA photochemotherapy, this also includes psoriatic erythroderma as well as pustular forms. Cutaneous T-cell lymphoma is a clonal proliferative disease of T helper cells which appears to be confined to the skin in its early stages. Vitiligo is pigmentary disorder of unknown etiology which is characterized by the loss of melanocytes and pigment from circumscribed areas of otherwise normal skin. One of these entities comprises individuals with end-stage renal disease who are commonly prepared for kidney transplants from living, related donors by receiving whole blood trans-fusions from the potential donor. Among the drugs of potential value, 8-methoxypsoralen appears to be merely the first of series of photosensitive compounds to be activated in plasma and blood cells.