The effect of inhibition of disaccharidases on the degree of absorption of glucose, lactose, and sucrose was examined utilizing an in vivo model in the rat. Acarbose, a competitive alpha-glucosidase inhibitor was utilized to selectively inhibit small intestinal mucosal enzymes. Adult rats (250-350 g body weight) were the subjects of intraduodenal bolus infusion experiments with either sugar alone or sugar plus acarbose. All sugars were infused at a dose of 0.5 g/kg body weight. Portal venous blood glucose was determined at 30-min intervals from 0 to 150 min. Glucose (monosaccharide) and lactose (beta-galactoside) absorption were not altered by the presence of acarbose. In contrast, sucrose (alpha-glucosidase) absorption was significantly diminished in the presence of acarbose. Sucrose absorption in the presence of increasing acarbose doses (0.7-5.6 mg/kg body weight) was depressed in a dose-dependent fashion. Linear regression analysis revealed a high degree of correlation between residual sucrase activity and area under blood glucose curve (r = 0.9837). Similar degrees of correlation were found between acarbose dose and area under blood glucose curve (r = -0.9322), and between residual sucrase activity and acarbose dose (r = -0.9695). These data confirm that acarbose is a selective alpha-glucosidase inhibitor that does not affect monosaccharidase transport. In the presence of acarbose, alpha-glucosidase absorption is diminished in a dose-dependent fashion. Postprandial glucose rise following an alpha-glucosidase meal seems to be determined, in the presence of graded acarbose inhibition, by residual mucosal alpha-glucosidase activity.