Failure to respond or development of intolerable side effects to at least one of the following treatments: sulfasalazine, gold retinoids, PUVA, methotrexate, azathioprine or cyclosporin. A waiting period of equal to or greater than 4 weeks after the end of previous systemic treatment will be required before initiation of fludarabine treatment. Topical treatment for psoriasis (glucocorticoids, tar, anthralin, etc.) should be discontinued 2 weeks prior to study entry.