AbstractThe intestinal microvillar enzyme complex sucrase‐isomaltase has been studied in cystic fibrosis and control ileum. A number of biochemical parameters of the enzyme in ileum homogenates have been determined. Both solubilized as well as membrane‐bound sucrase‐isomaltase were analyzed with respect to their reaction with monoclonal antibodies against human sucrase‐isomaltase. Finally the subcellular localization of sucrase‐isomaltase was verified by immunoelectronmicroscopy or via the analysis of purified brush‐border membrane preparations. At all levels no significant differences could be detected between sucrase‐isomaltase of cystic fibrosis and control ileum. It is concluded that an abnormal subcellular localization and/or abnormal enzymatic activity of sucrase‐isomaltase in cystic fibrosis intestine cannot explain the markedly decreased disaccharidase activities in amniotic fluids from pregnancies resulting in a child affected with cystic fibrosis.