At 3 weeks after jejunal-bypass operation in the rat, the proximal ileum exhibited a greater sucrase specific activity than did sham-operated controls, whereas isomaltase activity was unaffected. Electroimmunoassay of sucrase-isomaltase and a degradation product, isomaltase monomer, revealed an elevated molar ratio of sucrase subunit to isomaltase subunit in operated rats, suggesting a decrease in the extent of degradation of ileal sucrase-isomaltase after the jejunal-bypass operation.