ICP being a very significant parameter of intracranial pathology, it needs to be recorded continuously. ICP of 7 cases of normal pressure hydrocephalus (NPH) and 6 postoperative patients, for whom relationship between REM sleep and ICP was under discussion, was monitored at night and recorded by Brock's method. Polygraphic records also were obtained. Increased ICP was related to REM sleep in 3 of 6 postoperative cases. In the remaining 3 cases, REM sleep could not be observed the first postoperative night, and ICP was lower and stable all night. This fact may be an effect of anesthetic drugs. NPH patients were divided into 2 groups by pressure profile during night recording of ICP. One group of 2 cases demonstrated irregular ICP during REM sleep while the other group of 5 cases did not. The former 2 cases showed neurological improvement after shunt operations. In NPH cases, ICP has significance in deciding whether surgery is necessary. It appears reasonable to suggest that the augumentation of ICP during REM sleep in cases of hydrocephalus and postoperative condition is related to an increase in cerebral blood flow and an exhaustion of the absorptive mechanisms of CSF.