In visceral organs of mammals, most noxious (painful) stimuli as well as innocuous stimuli are detected by spinal afferent neurons, whose cell bodies lie in dorsal root ganglia (DRG). One of the major unresolved questions is the location, morphology and neurochemistry of the nerve endings of spinal afferents that actually detect these stimuli in the viscera. In the upper gastrointestinal (GI)-tract, there have been many anterograde tracing studies of vagal afferent endings, but none on spinal afferent endings. Recently, we developed a technique which now provides selective labeling of only spinal afferents. We used this approach to identify spinal afferent nerve endings in the upper GI-tract of mice. Animals were anesthetized and injections of dextran-amine made into thoracic DRGs(T8-T12). Seven days post-surgery, mice were euthanized, the stomach and esophagus removed, fixed and stained for Calcitonin Gene Related Peptide (CGRP). Spinal afferent axons were identified which ramified extensively through many rows of myenteric ganglia and formed nerve endings in discrete anatomical layers. Most commonly, intraganglionic varicose endings (IGVEs) were identified in myenteric ganglia of the stomach and varicose "simple-type" endings in the circular muscle and mucosa. Less commonly, nerve endings were identified in internodal strands, blood vessels, submucosal ganglia and longitudinal muscle. In the esophagus, only IGVEs were identified in myenteric ganglia. No intraganglionic lamellar endings (IGLEs) were identified in stomach or esophagus. We present the first identification of spinal afferent endings in the upper GI-tract. Eight distinct types of spinal afferent endings were identified in the stomach; most were CGRP-immunoreactive. This article is protected by copyright. All rights reserved.