In order to understand the pathogenesis of increased intracranial pressure, the concept of the driving pressure (DP) from the intracranial vascular system was proposed. The DP consists of the transmission of atrial pressure (ADP) and venous pressure (vp). It is well known that when the animals died, the intracranial pressure decreased to the atmospheric pressure. This means that the DP is important in maintaining the static pressure of the cerebrospinal fluid. The theoretical equation of the intracranial pressure was expressed as follows.ICP=ADP+VP (1) ADP is expressed as (2). ADP=eta (BP-VP) (2) The pressure transmission rat (eta) was calculated as the ratio of the CSF pressure to the systemic arterial blood pressure in the experimental and clinical cases. In the normal CSF pressure, eta was very small (2.0 X 10(-2)), while in the severe intracranial hypertension, eta approached to 1. The concept of the driving pressure was useful to analyze the static intracranial pressure and the pulse pressure.