After a short description of the morphology of the small intestinal mucosa the physiological processes of carbohydrate digestion and absorption are discussed. While starch is hydrolyzed by amylase in the lumen of the duodenum, the disaccharide hydrolysis does not take place in the intestinal lumen, but at the brush border membrane of the enterocyte. The liberated monosaccharides are--at least in part--absorbed by a specific active transport system. This mechanism is different from those which are responsible for the active transport of primary monosaccharides, i.e. monosaccharides which do not result from oligosaccharide hydrolysis. The exit process for monosaccharides out of the enterocyte into the extracellular space occurs by "facilitated diffusion". Passage through "fenestrated" capillaries is discussed as a possible mechanism for the entry of monosaccharides into the blood vessel system.