Zinc (Zn), copper (Cu) and magnesium (Mg) concentrations in cerebrospinal fluid (CSF) and serum were determined with atomic absorption spectrophotometry in 74 patients suffering from various neurological diseases, and in 28 healthy controls. Increased CSF zinc levels were found in the group of peripheral nervous system diseases (P less than 0.01) and in the cases of different neurological syndromes with increased CSF protein concentration (P less than 0.001). Increased CSF and serum copper levels were found in the cases with increased CSF protein levels (P less than 0.05). It is probable that the damaged blood-brain-barrier (BBB) permits the passage of the trace elements Zn, Cu and of Mg into the subarachnoid space. Decreased serum Cu levels (P less than 0.01) were found in the group of multiple sclerosis (MS). The findings are correlated to those of previous communications.