In conscious dogs bilateral carotid occlusion increased arterial pressure by similar amounts at rest (+ 27 mmHg) and during graded exercise (+ 29 mmHg). During exercise stimulus-response curves for arterial pressure and heart rate derived from isolated carotid sinuses were displaced upward proportionately to the work load, but the curve characteristics were unchanged. After acute bilateral vagotomy similar responses to carotid occlusion were obtained at rest (+ 85 mmHg) and at 21% grade (+ 84 mmHg); the range and maximal slope of the arterial pressure stimulus-response curve during exercise was similar to that at rest, but the exercise curve was displaced downward and to the left. It was concluded that the carotid baroreflex was able to modulate arterial pressure as well during running as at rest. Dogs with neither carotid, aortic, or cardiopulmonary receptors able to respond to the exercise stress became and remained hypotensive during mild exercise; during severe exercise hypotension was present initially, but after 90 s arterial pressure recovered toward the preexercise level. The data indicated that arterial and cardiopulmonary baroreceptors have a major role in the support of arterial pressure in the first moments of exercise.