The activities of intestinal disaccharidases are known to be responsive to changes in the dietary intake of carbohydrates in the adult rat. Little is known, however, regarding the activities of these enzymes in obese subjects and how they are affected by differing carbohydrate intakes. To evaluate the effect of carbohydrate intake on the activity of intestinal disaccharidases in obesity, we used the genetically obese mouse C57BL/6J obob as an experimental model. Representing an example of early-onset obesity and mature-onset diabetes, this animal is characteristically hyperinsulinemic and hyperglycemic. Groups of obese mice and lean littermates were fed for 7 weeks equal amounts of either high-dextrose or low-dextrose isoenergetic diets. Sucrase, maltase, and lactase activities were measured on intestinal homogenates from the proximal and middle portions of the jejunoileum (upper and lower jejunum). Results were expressed as activity per tissue protein as well as total activity. Obese mice were found to have consistently greater total activity of both sucrase and maltase than their lean littermates, mostly as a result of increased intestinal size. Total lactase activity, however, was similar in the upper jejunum in both obese and lean mice, largely related to a decreased specific activity in obese mice. All mice fed the high-dextrose diet had significantly increased total activity of all disaccharidases studied when compared to the low-dextrose-fed animals, except for the lactase activity in the lower jejunum, where no differences were found in either group. Increases in activity related to high carbohydrate intake were a result of increases in specific activity.