Infantile hypertrophic pyloric stenosis (IHPS) a common childhood disorders characterized by nonbilious projectile vomiting, an olive shaped mass in the right upper quadrant of the abdomen and visible gastric peristaltic wave in the upper abdomen. Its etiology and pathogenesis are not clear but abnormal nerve distribution of the pylorus has been postulated^2-6. We performed immunocytochemical staning to the pyloric muscle from 10 IHPS and 3 controls patients, utilizing specific monoclonal antibody to NCAM(neural cell adhesion molecule). In IHPS patients, the number of NCAM protein immunoreactive nerve fibers were less than that in normal subjects. Auerbach myenteric plexuse was well developed and interbundle nerve plexuse was present but nerve fibers supplying individual muscle cells in smooth muscle bundles were poorly developed. These results indicate reduction of innervation in smooth muscles in IHPS patients that possibly contributes to the pathogenesis of IHPS.