Proton magnetic spectroscopy (1H-MRS) investigation was performed on CSF samples of patients with neurological inflammatory diseases including 52 cases of multiple sclerosis (MS). 12 acute idiopathic polyneuropathies, 20 acute meningitides (10 viral and 10 bacterial). Spectra were compared with those acquired in 18 neurological controls. High CSF lactate levels were found in MS patients during clinical exacerbation of relapsing-remitting course (p = 0.036 vs neurological controls). In MS patients with MRI evidence of Gd-enhanced plaques CSF lactate was higher than in patients with MRI inactive plaques (p = 0.017). CSF lactate positivity correlated with number of CSF mononuclear cells in MS patients with clinical activity (p = 0.05) as well as in MS patients with MRI enhancement (p = 0.003). A comparative 1H-MRS investigation in vivo on localized demyelinating areas confirmed an elevated lactate signal in Gd-enhanced (61%) more frequently than in unenhanced (22%) plaques (p = 0.03). MS patients with high lactate signal in active plaques showed high lactate levels in CSF. Increased CSF lactate was found also in patients with acute meningitis and idiopathic polyneuropathy. These data suggest that changes in lactate levels may depend on anaerobic glycolytic metabolism in activated leukocytes during inflammatory diseases. A decrease of CSF formulate levels was found in MS patients during active and inactive clinical phase (p = 0.037, p=0.05 vs neurological controls respectively). Formate changes might be related to a disorder of choline-glycine cycle in MS. 1H-MRS in vivo showed significant increase of choline in acute plaques, whereas a decrease of N-acetyl aspartate was found in chronic plaques; these metabolites are undetectable in CSF. CSF glucose levels were lower in bacterial than in viral meningitis (p = 0.014) and in neurological controls (p = 0.05). These observations suggest that 1H-MRS may be able to detect CSF metabolic impairment in neurological inflammatory diseases. In MS some CSF findings reflect metabolic changes occurring in brain demyelinating areas, and they could be useful foe evaluation of disease activity in different stages of disease evolution.