In recent years a role has been recognized for fibroblast growth factor (FGF)-2 in the pathogenesis of demyelination and the failure of remyelination in experimental models of multiple sclerosis (MS). FGF-2 levels were determined using a sensitive immunoassay in the cerebrospinal fluid (CSF) of 20 patients with clinically isolated syndrome (CIS), 40 patients with relapsing-remitting (R-R) MS, and 30 patients with secondary progressive (SP) MS, correlated with MRI measures. Control CSF samples were obtained from 20 subjects who underwent lumbar puncture for diagnostic purposes and for whom all instrumental and laboratory analyses excluded systemic and nervous system diseases. FGF-2 levels in the CSF of MS and CIS patients were significantly higher than controls (P<0.001 and P<0.05, respectively). The highest levels were detected in R-R MS patients during relapse and in SP MS patients with an increase of 1 point in EDSS scores in the last 6 months. A significant correlation was found in SP MS patients with lesional load (R=0.43, P<0.01) but not with parenchymal fractions as measures of brain atrophy. A slight increase in serum FGF-2 levels was also found in R-R MS patients during relapse with gadolinium enhancing lesions and in SP patients with disability progression. These findings support the implication of FGF-2 in the pathogenesis of MS and concur with recent reports of the involvement of FGF receptor signalling in the disruption of myelin production in differentiated oligodendrocytes and in the loss of adult oligodendrocytes and myelin in vivo due to FGF-2.