Thirty five head injured patients were subjected to day-by-day monitoring of intracranial pressure (ICP), arterial blood pressure (ABP) and blood flow velocity (FV) in middle cerebral artery. Parameters describing cerebral autoregulation: flow velocity time average, systolic, diastolic values, pulsatility index (PI), estimate of cerebrovascular resistance (CVR = CPP/FV) etc. were analyzed as functions of CPP (ABP-ICP). The results show that for CPP below 55 mmHg the evidence of exhausted autoregulation can be observed in FV, CVR, PI. The method is helpful in assessment ot the optimal level of CPP in order to reduce the probability of ischaemic brain insults.