In order to investigate the manner in which bilateral carotid sinus pressoregulatory signals are summated in the reflex loop, the relationship between systemic arterial pressure changes (ΔSAP) caused by unilateral and bilateral intrasinusal pressure changes (ΔISP) in the carotid sinuses was examined in 27 dogs. ISP was altered by either isolating the sinuses and changing the perfusion pressures (8 dogs) or occluding the common carotid arteries (19 dogs). The results from the isolated perfused sinus experiments showed conformity between the sum of two ΔSAP's during left- and right-side ISP changes and the actual ΔSAP during bilateral ISP change. Accordingly, it is concluded that the process of summation of carotid sinus static pressoregulatory signals is one of simple addition, at least within the investigated physiological pressure range. Other important findings were as follows: a) The mean open-loop, over-all gains of the left and right unilateral sinus pressoreceptor reflexes were –0.40 and –0.68, respectively, as measured in the isolated sinus experiment using small input pressure changes, the left-to-right gain ratio being 0.59; similar values were found in the carotid occlusion experiment. b) The bilateral over-all reflex gain was –0.99, and vagotomy increased this to –1.51, which is probably a value close to the true static open-loop gain of the carotid sinus pressoregulatory reflex in the normal pressure range of anesthetized dogs.