The present study investgated if constitutive nitric oxide synthase(cNOS), especially neuronal type, is expressed in gastrointestinal epithelial cells of rat. Expression of cNOS was immunohistochemically determined. Some gastric epithelial cells were found to express cNOS. Although less than that by the gastric epithelial cells, cNOS was also found to be expressed by the intestinal epithelial cells. Thus it is possible that constitutive type of nitric oxide synbthase in gastrointestinal epithelial cells may play a role in normal gastrointestinal function.