Virtual reality enables people to behave and feel as if they were present in a virtual environment and therefore is a useful tool in many fields. In order to study the usefulness of virtual environments, the concept of presence is examined. Up to now, the most common method to measure presence has been to use subjective measures based on validated questionnaires about user experience. However, more objective measurements, such as physiological measurements, are now being considered. In this study, transcranial Doppler (TCD) sonography is presented as a brain activity measurement technique that can be used to study presence in virtual environments. Thirty-two subjects navigated in a virtual environment in different immersive conditions while TCD was monitored. The results show that there are changes in blood flow velocity in the subjects during moments associated with different levels of presence.