To define the myenteric plexus along the human gastrointestinal tract, we studied three neonatal and six adult specimens, postmortem, by silver impregnation. There were no clear differences between the neonatal and the adult gastrointestinal tracts. In the body of the esophagus, the plexus was sparse, with few ganglia; 30%-40% of fascicular intersections were devoid of ganglia. In the lower 5 cm, the esophagus had thick bundles of nerve fibers ("shunt fascicles"), which crossed the gastroesophageal junction and radiated to the periphery of the stomach through several branches. The plexus in the stomach was uniform, with intermediate and intrafascicular ganglia. A thick nerve bundle encircled the pylorus and gave branches on either side to the antrum and the duodenum. Shunt fascicles in the stomach did not cross the pylorus but extended to the distal antrum. In the duodenum and proximal jejunum, the plexus was regular, but in the mid-small intestine, the longitudinal interganglionic fascicles were more prominent than the circumferential fascicles. Distally, this pattern was reversed; circumferential fascicles were more prominent and ganglia were dense in the terminal ileum. Thin, short shunt fascicles were scattered along the entire small intestine, becoming more abundant in the terminal ileum. Short, thick shunt fascicles traveled proximally from the ileocecal junction for about 25-30 cm. As in the stomach, shunt fascicles did not cross the ileocecal junction, but a thick nerve bundle encircled it. In the cecum and proximal colon, the plexus was sparse with large intermediate and intrafascicular ganglia. In the rectum and distal colon, the plexus was dense, with parafascicular and intrafascicular ganglia. Long ascending nerves extended from the distal rectum into the midcolon. In addition, there were short, thick nerve bundles in the rectum that traveled proximally.