This study has utilized unilateral physiological pressure stimulation f a vascularly isolated carotid sinus combined with c-fos immunohistochemistry to locate neurons of the nucleus tractus solitarius which are activated by carotid baroreceptors in the anesthetized, vagotomized dog. Carotid baroreceptor stimulation primarily activated neurons in the ipsilateral commissural and medial subnuclei of the caudal nucleus tractus solitarius. In the intermediate and rostral nucleus tractus solitarius, carotid baroreceptor stimulation activated neurons in the dorsal and medial subnuclei. Results from this study also suggested that different subgroups of nucleus tractus solitarius neurons may be activated by baroreceptors with different pressure thresholds. The use of c-fos immunohistochemistry in this study has enabled the definition of populations of dorsal medullary neurons in the carotid baroreflex pathway. The results also suggest a different projection of carotid baroreceptors with different pressure thresholds.