AIM To study the colon innervation of trisomy16 mouse, an animal model for Downssyndrome, and the expression of protein geneproduct 9.5 ( PGP 9.5) in the stenosed segmentof colon in Hirschsprungs disease (HD).METHODS Trisomy 16 mouse breeding;cytogenetic analysis of trisomy 16 mice; andPGP 9.5 immunohistochemistry of colons oftrisomy 16 mice and HD were carried out.RESULTS Compared with their normalIittermates, the nervous system of colon intrisomy 16 mice was abnormally developed.There existed developmental delay of muscularplexuses of colon, no submucosal plexus wasfound in the colon, and there was 5mmaganglionic bowel aparting from the anus intrisomy 16 mice. The mesentery nerve fiberswere as well developed as shown in their normallittermates. Abundant proliferation of PGP 9.5positive nerve fibers was revealed in thestenosed segment of HD colon.CONCLUSION Trisomy 16 mice could serve asaganglionic bowel in the distal part of colon.Abundant proliferation of PGP 9.5 positive fibersresulted from extrinsic nerve compensation,since no ganglionic cells were observed in thestenosed segment of the colon in HD. HD has agenetic tendency.