The products of jejunal mucosal exfoliation in infants have been collected from the intestinal lumen by the method of intestinal perfusion. The brush border materials collected in the perfusion solutions have been separated into three fractions by differential centrifugation. The first fraction contained intact brush borders, including those still attached to degenerating cells, and large brush border fragments. The second fraction was mainly composed of split microvilli. The third fraction contained amorphous residues of the microvilli. The specific activities of sucrase in the total perfusion solution materials and in the microvillous (second) fractions were comparatively not much lower than those reported, respectively, in mucosal biopsies of infants and children and in highly purified microvillous membranes from human intestine. These findings indicate that sucrase is retained to a certain extent on the microvillous surface during cell desquamation and breakage.