Several clinical studies have shown that systemic therapy with fumaric acid esters (FAEs) in patients with moderate to severe psoriasis is effective and has a good long-term safety profile. For therapeutic use, tablets with a defined mixture of FAEs (dimethylfumarate [DMF] and three different salts of monoethylfumarate) are registered in Germany. There is evidence that DMF is the most essential component in this formulation with an antipsoriatic effect. Currently, there are few data on the pharmacokinetics of fumarates in human beings. DMF seems to act as a prodrug for its main metabolite: monomethylfumarate. This hypothesis was supported by the observation that only monomethylfumarate was detected in the plasma of human beings after the oral administration of FAEs. FAEs have been tested in different biological assays, and effects such as inhibition of the nuclear factor kappa B pathway or induction of apoptosis by DMF have been described. For these data, the role of DMF as a modulator of intracellular glutathione plays an important role.