Neurotoxic properties of manganese (Mn) are well documented. It is less known that Mn contributes to the development of neurodegenerative disorders in the general population. This study presents Mn data from patients with amyotrophic lateral sclerosis (ALS) in a well-defined cohort diagnosed by electrophysiological methods. Cerebrospinal fluid (CSF) and plasma were collected from patients and controls. Mn concentrations were analyzed by high-resolution inductively coupled plasma mass spectrometry. Concentrations of Mn were significantly higher in ALS CSF (median 5.67 mu g/L) than in CSF from controls (median 2.08 mu g/L). Also, ALS CSF Mn concentrations were higher than ALS plasma Mn concentrations (median 0.91 mu g/L), suggesting transport of Mn into the central nervous system. The properties of barrier systems between blood and the brain are discussed and the possibility of Mn accumulation contributing to the relentless course of ALS is introduced.