To the Editor.Ìý —A recent report from Stern and coworkers¹ showed a positive relationship between the 3-methoxy - 4 - hydroxy - phenethyleneglycol (MHPG) level in cerebrospinal fluid and an increased reaction time (RT) in Parkinson's disease (PD), and an altered norepinephrine metabolism was suggested. Ten consecutive patients with idiopathic PD were selected according to the following criteria: normal score in Mini-Mental State examination, symptoms present for less than six years, Hamilton Depression Scale score within normal limits, and a maximal score of 10 on the Northwestern University Disability Scale. All patients performed the simple RT and choice RT tests. Each patient underwent a lumbar puncture to measure cerebrospinal fluid concentrations of the metabolites of norepinephrine (MHPG), serotonin (hydroxyindoleacetic acid [HIAA]), and dopamine (homovanillic acid [HVA]) by means of high-performance liquid chromatography with amperometric detection. The study was performed twice; first, with patients receiving their regular levodopa regimens and, second, eight