Abstract— —The concentration of free amino acids has been determined in lumbar CSF in 37 fasting normal subjects. The values obtained have been compared with the concentration of the same amino acids measured in venous plasma collected simultaneously and with ventricular CSF amino acid concentrations. Twenty‐three amino acids have been identified and quantitated in CSF and plasma. Trace quantities of eight other amino acids have been also detected. The concentration of 13 amino acids in CSF has been shown to be directly related to the plasma concentration. No such relationship was noted for the other 7 amino acids. Significant variations in the concentration of individual amino acids relating to both age and sex have been noted. A large number of unidentified ninhydrin positive compounds have been found in CSF. Preliminary studies have identified one of these as ɛ‐aminobutyric acid (GABA).

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SUMMARY Measurements of cerebrospinal fluid (CSF) and plasma amino acid concentrations have been made in 12 patients with the Guillain-Barre syndrome. The CSF protein concentration was normal in seven specimens and raised in 13. Abnormalities of the CSF amino acid profile were found in all specimens but were more marked in those with a raised CSF protein concentration. The possible causes and diagnostic significance of these changes are discussed.