Specific high-affinity neurotensin binding sites were labeled in sections of the rat caudal brainstem using a monoiodinated ligand, and their distribution was examined by light microscopic radioautography after fixation with glutaraldehyde. In the medulla, labeled binding sites were mainly concentrated within the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, the external cuneate nucleus, the lateral reticular nucleus, the medial vestibular nucleus, the retrofacial nucleus, the linearis nucleus, the paragigantocellular nucleus and the nucleus raphe pallidus. Within the pons, neurotensin binding sites were detected in the reticulotegmental nucleus, the pontine nuclei, the dorsal tegmental nucleus, the laterodorsal and pedunculopontine tegmental nuclei and the nuclei raphe dorsalis and medianus. Most nuclei found here to contain high densities of neurotensin binding sites have been shown to stain intensely for acetylcholinesterase, suggesting a possible association between this enzyme and neurotensin receptors.