We describe for the continuous recording of CSF pressure a method in which a polyethylene catheter is introduced into the subarachnoid space. The pressure is shown on a polygraph by means of a recording apparatus. The technique can be applied to patients with subarachnoid haemorrhage, ischaemic infarcts, supratentorial space occupying lesions, or communicating hydrocephalus. The accuracy and limitations of the technique are discussed.