The examination of the spinal fluid has become almost as routine a procedure in the diagnosis of neuropsychiatric problems as that of the blood in internal medicine. When the great amount of valuable information made available to the diagnostician is considered, an occasional unfortunate sequel may be forgiven, especially if an effort is made to prevent its recurrence. The most common disabling event, the result of a lumbar puncture, is the headache, neck ache and vertigo that frequently ensue, particularly if a large needle is used and the patient is permitted to go about his business in a few hours. Temporary meningitic signs are sometimes observed, probably resulting from an outpouring of the cells into the subarachnoid space. It is known that a second lumbar puncture performed some hours after a diagnostic tap will show an increase of lymphocytes and albumin in the spinal fluid. Furthermore, if the tap has