Brainstem projections of the aortic nerve in the rat were studied using the transganglionic transport of horseradish peroxidase. Labeled axons were found to project predominantly to the ipsilateral interstitial nucleus and to the ipsilateral dorsolateral aspect of the nucleus of the solitary tract near the level of the obex. Lighter bilateral projections were also found to the medial, ventrolateral and dorsolateral aspects of the solitary complex, and to the commissural nucleus. These data provide evidence of direct aortic baroreceptor afferent projections to restricted regions of the solitary complex and indicate that these specific areas function in the integration of the baroreceptor reflex.