The extent to which estimations of intracranial pressure can be derived from intracranial flow patterns was studied. The blood flow velocity in the middle cerebral artery was recorded with the EME TC 2-64 transcranial Doppler (TCD) device in 26 patients suffering from various severe cerebral diseases. Simultaneously the mean intracranial pressure (ICP) was measured by means of an epidural device. Arterial carbon-dioxide tensions were monitored by blood gas analysis. In all patients it was observed that the middle cerebral artery flow patterns changed distinctly when the ICP increased; these changes were distinguished by a decrease of the mean flow velocity and an increase of the Pourcelot index. A good correlation between the ICP and the flow parameters (especially the product mean systemic arterial pressure x Pourcelot index/mean flow velocity) was found in a select group of 13 patients, in whom comparable initial conditions existed and in whom additional parameters influencing the TCD recordings could be kept constant (r = 0.873; P less than 0.001).