The primary goal of this study was to determine if differences in proton magnetic resonance spectroscopy signals exist between normal appearing white matter (NAWM) of multiple sclerosis (MS) patients and white matter of control subjects. Water suppressed proton magnetic resonance spectroscopic imaging was used to determine the signal intensities of N-acetylated moieties (NA, predominantly N-acetylaspartate (NAA) the putative neuronal marker), creatine and phosphocreatine (Cr), and cholines (Ch) in 19 MS patients (15 relapsing-remitting and four secondary progressive) and 19 age matched control subjects. NA/Cr was significantly reduced (P < 0.001) in MS NAWM (1.8 +/- 0.2; x +/- s.d.) distant from MRI detected lesion areas compared to white matter of control subjects (2.1 +/- 0.2). This reduction was due to an increase in Cr from 0.39 +/- 0.04 (arbitrary units) in controls to 0.45 +/- 0.05 in MS patients. There was no significant change in NA or Ch in MS NAWM compared to controls. NA/Cr, distant from MRI lesion, was negatively correlated with total brain lesion volume as measured from T2-weighted MRI. We interpret the reduced NA/Cr in MS NAWM to indicate diffuse microscopic disease.