Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS), characterized by accumulation of mononuclear cells. The pathogenesis of MS is complex and probably involves soluble immune mediators, particularly cytokines, and activated memory T cells, that are thought to migrate into the CNS. During lesion formation in MS, cytokines regulate cell functions, such as cell recruitment and migration. Because the chemokine RANTES play a role in both activating and recruiting leucocytes, particularly memory T cells into inflammatory sites, the authors have assessed RANTES mRNA levels at the site of lesions. Expression levels were analysed in brain samples and compared with neurological, infectious and other controls. RANTES was expressed by activated perivascular memory T cells, predominantly located at the edge of active plaques. While RANTES mRNA was detected in all 17 MS brains analysed, it was only found in six of the 14 control patients and generally at a lower expression level. In view of the regulatory and chemotactic properties of RANTES, these results imply that RANTES in MS lesions may play an important role in the activation and/or selective accumulation of memory T cells and, thereby, in the pathogenic events associated with MS.