Midgut infusions of sucrose and other disaccharides were compared with monosaccharides for their effects on intestinal mucosal growth in rats otherwise maintained on total parenteral nutrition for 7 days. Mucosal mass progressively increased in a proportional relationship to the concentration of infused sucrose. At equal concentrations by weight, disaccharide infusions stimulated mucosal growth more than monosaccharides. Disaccharide-induced mucosal adaptation was abolished when there was no hydrolysis of the disaccharide. The results suggest that the functional work load of absorbing epithelium, including the "work of hydrolysis," plays an important role in the stimulus for intestinal adaptation.