Maltose, malto-oligosaccharides and their reduced sugar analogues have been tested as substrates and inhibitors of human salivary alpha-amylase and small intestine alpha-glucosidases. - Maltotriose and maltotetraose as well as their reduced analogues inhibited competitively alpha-amylase. Maltitol, maltotriitol and maltotetraitol were not hydrolyzed. - The small intestine maltases hydrolyzed maltitol at a very low rate, but maltotriitol was split almost at the same rate as maltotriose. These three sugars were weak mutual inhibitors. - The small intestine glucoamylase was slightly inhibited by maltotriitol but not by maltitol whereas fungal glucoamylase activity was strongly competitively inhibited by maltitol. This study shows that where the reducing end glucose unit of the malto-oligosaccharides below five glucose units are converted into sorbitol, their inhibitory effect is retained but their capacity of hydrolysis is reduced or disappears.