The intraluminal mucous gel layer across the small intestine of rats aged 3 days, 1, 2, 4 and 6 weeks (n=10x5) was studied to investigate its postnatal development. Celloidin stabilisation of dried cryostat sections of small intestine, with the luminal contents, preserved the intraluminal mucous gel layer for staining by the periodic acid-Schiff reaction. Morphological differences in the mucous gel, between the villi of the small intestine, in rats of several postnatal ages were observed, most notably after the age of 2 weeks. The adhesive mucous gel layer, covering the intestinal epithelium in the small intestine, appears to undergo rapid development after weaning.