Alkali-extractable cereal arabinoxylan and oligosaccharides of known structure derived from it by enzymic hydrolysis were treated with endo-(1-->4)-beta-D-xylanases I and III from Aspergillus awamori CMI 142717 and the digests subjected to analysis by high performance anion-exchange chromatography. Clear differences in the mode of action of the two endo-(1-->4)-beta-D-xylanases were observed. When counting from the reducing end, at least one unsubstituted xylopyranosyl residue adjacent to singly substituted xylopyranosyl residues or two unsubstituted xylopyranosyl residues adjacent to doubly substituted xylopyranosyl residues cannot be removed by endo-(1-->4)-beta-D-xylanase I. At least two unsubstituted xylopyranosyl residues adjacent to singly or doubly substituted xylopyranosyl residues cannot be removed by endo-(1-->4)-beta-D-xylanase III. beta-D-Xylosidase from the same xylanolytic system was able to remove terminal xylopyranosyl residues from the nonreducing end of branched oligosaccharides only when two contiguous unsubstituted xylopyranosyl residues were present adjacent to singly or doubly substituted xylopyranosyl residues.