The internal jugular (IJ) valve is the only valve between the heart and the brain, preventing venous reflux into the IJ vein. Internal jugular valve competence has been tested by IJ venography. Doppler ultrasonography of the IJ vein and M-mode ultrasonography of the IJ valve, and color flow imaging (CFI) of the IJ vein. However, interpretation of venous Doppler and CFI is difficult, and venography is invasive. The purpose of this study was to evaluate the feasibility of a new dynamic method to test IJ valve competency, and to review the literature regarding the potential clinical importance of this pathophysiology. Ten patients had intravenous injection of agitated air and saline during Valsalva maneuver with B-mode monitoring and CFI of the right IJ vein. Contrast bubbles were clearly identified refluxing into the right IJ vein in 50% of patients. Air contrast studies more often showed IJ valve incompetence than CFI. Bubbles appeared in the IJ vein within 19.2 sec and persisted up to 282 sec. Bubble aggregation was also observed. There was no correlation between positive bubbles and the presence of spontaneous echo contrast on baseline B-mode imaging. Air contrast ultrasound venography (ACUV) is a new noninvasive method to assess competency of the IJ valves. This technique is feasible, appears to be more sensitive than CFI, and adds a new dimension to the study of the venous system in cerebrovascular disease. Potential clinical application includes evaluation of patients with increased central venous pressure, those with morning headaches, and those on positive end-expiratory pressure ventilators.