The ventricular system and subarachnoid spaces were studied with RIHSA (radioiodinated serum albumine) in 25 patients. A total of 75 scans were drawn; 3 on each patient. These scans were drawn 2, 6 and 24 hours after having administered RIHSA. The RIHSA was introduced into the lateral ventricle of 5 patients intended for the study of the ventricular system; into the cisterna magna of two patients, in order to study the intracranial and intraspinal subarachnoid spaces; in the other 18 patients it was injected by lumbar route for the study of the spinal canal. When the results obtained by the scintilography were compared with those shown by the orthodox neuroradiological methods the first ones showed high positivity, and even offered better information in some cases. This was especially true for the cases of arachnoiditis. It is possible to locate total or subtotal blocks of spinal canal as well as dmonstrate exactely its limits with only one intrathecal or cisternal introduction of RIHSA. No serious complications were observed. In one case o CSF pleocytosis developped without clinical symptoms; in another one, there was a leak of the substance through the puncture into the peridural space. This method offers high reliability in neurological diagnosis and does not produce serious complications.