The substrate specificity of the xyloglucanase Cel74A fromHypocrea jeco-rina (Trichoderma reesei) was examined using several polysaccharides and oligosaccharides. Our results revealed that xyloglucan chains are hydro-lyzed at substituted Glc residues, in contrast to the action of all known xyloglucan endoglucanases (EC ).