In 8 patients, beta-lipotropin (beta-LPH), beta-endorphin (beta-EP), ACTH, protein and chloride concentrations were measured in cerebrospinal fluid (CSF) samples obtained simultaneously from the lumbar space and lateral ventricle. Albumin and IgG levels were significantly higher in lumbar than in ventricular CSF samples while no craniocaudal gradient was observed for neuropeptide concentrations. The importance of molecular weight in determining such a regional distribution is supported also by the similar lumbar and ventricular levels of chlorides. These data would validate the CSF approach through lumbar puncture as a tool for exploring neuropeptides in the central nervous system.