A total of 21 patients with normal-pressure hydrocephalus were examined. Cerebrospinal fluid (CSF) was collected before and after operation with a ventriculoperitoneal shunt. A slight plasma-like protein pattern indicating a blood-brain barrier (BBB) dysfunction was seen in 38% of the patients before operation. No characteristic changes could be found in the "CSF-specific" protein fraction. After the shunt operation 65% of the patients had a BBB dysfunction to macromolecules and 70% had two additional acidic protein bands in the CSF-specific fraction. Ventricular CSF protein content was 73% of lumbar CSF content when shunts were patent. Isotope encephalography showed a radionuclide accumulation at the intracranial part of the shunt system, indicating that the BBB damage might be located round the shunt catheter.