The technique of segmental perfusion was applied in vivo to study the release of enzymes from the mucosa cells under the influence of bile salts. Five brush border membrane enzymes, five cytosolic, one mitochondrial and two lysosomal enzymes were measured. Spontaneous release (Ringer solution), due to their superficial localization, was greatest for enteropeptidase and alpha-glucosidase. 3 and 10 mmol/l sodium taurocholate, and 0.5 and 3.0 mmol/l chenodeoxycholate were used. Surprisingly, the majority of cytosolic enzymes was released to a greater extent than membrane enzymes. On the other hand, lysosomal or mitochondrial enzymes were low or absent in the perfusion medium, a finding that excludes a serious injury to the mucosa cells. It must be inferred, therefore, that cytosolic enzymes are regularly externalized during the digestive process, the glycocalyx perhaps being a common matrix for pancreatic, membrane-associated and cytosolic enzymes.