We applied the concept of "phase synchronization" from nonlinear dynamics to the complex relationship between intracranial pressure (ICP) and arterial blood pressure (ABP) signals. This method is based on multiresolution wavelet transform (MRWT) in which the signals are divided into different frequency bands. We examined ICP and ABP signals from anaesthetized dogs, exploring normal ICP and elevated ICP by 1∼3 ml injection of saline into the cerebral ventricles. Phase synchronization analyses show an interesting phenomenon of phase reset from relatively uniform phase distribution to phase clustering around 0° after injection. To further quantitatively measure phase synchronization, phase coherence is used to distinguish the dynamics of normal ICP and elevated ICP by saline injection. Elevated ICP exhibits higher phase coherence than that of normal ICP, The results suggest that the association between ICP and ABP may involve nonlinear mechanisms of regulation. The clinical application of this method is in investigation.