It has recently been suggested that the sulfidopeptide leukotriene C4 (LTC4), a 5-lipoxygenase product of the arachidonic acid metabolism and one of the most potent mediators of vascular permeability, might be involved in the pathogenesis of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS). Subsequently, 20 guinea pigs with EAE were treated with sulfasalazine, a substance with a proved leukotriene inhibiting effect, which has previously been described as exerting beneficial effects in patients with inflammatory bowel disease and rheumatoid arthritis. The sulfasalazine-treated guinea pigs showed a significantly better clinical outcome, as well as a significantly lower histological inflammation score compared with 19 controls.