Proton and phosphorus magnetic resonance spectroscopy of the brain was performed in 35 patients with degenerative cerebral disorders: 24 patients had demyelinating (white matter) disorders and 11 patients had neuronal (gray matter) disorders. Four grades of demyelination and three grades of cerebral atrophy were distinguished by magnetic resonance imaging criteria. The spectroscopic data were compared with normal values previously obtained. With increasing degrees of demyelination, lower ratios of phosphodiesters to beta-ATP were found. This trend was statistically significant. Decreased phosphodiester-beta-ATP ratios occurred simultaneously with imaging abnormalities. The decrease in phosphodiester-beta-ATP ratio in demyelinated areas is attributed to white matter rarefaction. Increasing cerebral atrophy was accompanied by lower ratios of N-acetyl aspartate to creatine. This trend was statistically significant. The decrease in the N-acetyl aspartate-creatine ratio was demonstrated before the magnetic resonance images showed signs of cerebral atrophy in patients with neuronal disorders. As N-acetyl aspartate is located exclusively in neurons and their branches, a decrease of the N-acetyl aspartate-creatine ratio can be attributed to neuronal and axonal damage and loss.