The currently licensed medications for relapsing-remitting multiple sclerosis (RRMS) are only partially effective and require a parenteral route of administration. Thus there is a need for new, preferably orally available therapeutics. Such a substance could be fumaric acid and its esters (FAE). These compounds are already in use for treatment of psoriasis and are known to have an immunomodulatory effect. In addition there is a potential for neuroprotective effects as suggested by in vitro studies and experiments in the animal model of experimental autoimmune encephalomyelitis. A phase II clinical study in RRMS patients with the modified fumaric acid ester BG-12 showed as "proof of principle" in a frequent MRI design that FAE significantly reduce the number of gadolinium-enhancing lesions after 24 weeks of treatment. Further phase III studies have been started to explore the long-term efficacy of this substance. The results of these studies will show if FAE can be another treatment option, maybe for combination therapy, in patients with MS.