Fumarate esters--an oral therapy for psoriasis--are used primarily in Europe, but not at all in the United States. Given that biological therapies are exceedingly expensive and pose an increased risk for infections and malignancy, the need for safer and less expensive therapies for psoriasis is compelling. Nonbiological therapies for psoriasis, including methotrexate and systemic retinoids, carry potentially severe side effects and relatively high cost. Fumarate, a natural product that is generated internally in humans during the Krebs cycle, is an attractive alternative to these therapies. However, the mechanism for fumarate's activity in psoriasis remains unknown.