1. The effects of changing intravascular pressures on integrated ear sympathetic nerve activity (ESNA) were studied in anesthetized artificially ventilated rabbits by inflating aortic and inferior vena caval perivascular balloons under conditions of normal arterial Po2 and during arterial hypoxia. 2. At normal Po2 ESNA was unaffected by arterial and cardiopulmonary baroreflex influences. The small inhibition of ESNA observed during rises in arterial pressure after vagotomy was also present after section of the carotid sinus and aortic nerves, and after cutting both vagi as well. 3. During hypoxia there was marked inhibition of ESNA, which was minimally influenced by vagotomy but abolished by section of the carotid sinus and aortic nerves, suggesting that it was chemoreceptor-mediated. There was a pressure-related rise in ESNA which was abolished by vagotomy and considered to be due to a central nervous chemoreceptor-cardiopulmonary baroreflex interaction.