Previous studies using magnetic resonance spectroscopy have shown that N-acetylaspartate (NAA) levels are reduced in the brains of patients with amyotrophic lateral sclerosis (ALS). New research indicates that this change is accompanied by an increase in serum levels of NAA, perhaps owing to release of this molecule from damaged neurons into the circulation. Serum NAA levels correlated significantly with ALS progression rates, suggesting a possible application as a biomarker for this condition.