1. Hydrolysis of N-benzoyl-l-tyrosyl-p-aminobenzoic acid (PABA-peptide) has been measured in soluble and particulate fractions of human small intestinal mucosa.
2. Both soluble and particulate fractions contained enzymic activity capable of splitting the PABA-peptide. In the paniculate fractions this activity increased threefold towards the distal small intestine.
3. Neither soluble nor paniculate activity was inhibited by the chymotrypsin inhibitor 1-chloro-4-phenyl-3-l-toluene-p-sulphonamidobutan-2-one (TPCK).
4. Column chromatography on Sephacryl S-300 resolved a peak of PABA-peptide hydrolase activity that was clearly distinct from other known brush-border peptide hydrolases and from added chymotrypsin standard.
5. This PABA-peptide hydrolase thus represents a distinct intestinal enzyme, possibly bound to the brush-border membrane, which could account for the residual urinary PABA recovery observed in patients and animal models with exocrine pancreatic insufficiency.