Cerebrospinal fluid pulsation is likely to be responsible for the progression of some diseases, and it is differences in pressure which are significant in causing the imposition of energy upon tissues. The normal range of such differences has not been extensively documented. A technique for measuring intracranial and intraspinal pressures simultaneously in erect conscious patients is described. Normally the pressures are in a continual state of pulsation in response to changes in pressure in the arteries and veins. The measurements of CSF pressure fluctuations in response to normal cardiac pulsation, respiratory changes, coughing, Queckenstedt's test, and a variation of Valsalva's manoeuvre have been recorded, and the physiology has been discussed.