A range of enteric polymeric molecules of different molecular masses and chemical structures were coupled to the protease Esperase (EC 3.4.21.62) using carbodiimide. The activities of the range of chemically modified enzymes of enlarged molecular weight were measured with a standard assay on casein as substrate. Gel filtration confirmed covalent bonding had taken place. Using the same activity value per gram of fibre, the range of modified enzymes were used to treat wool to see if the size of the enlarged enzyme would effect the location of enzyme attack and penetration ability. Less fibre damage in terms of weight loss and tensile strength of treated wool was observed for all six modified enzymes and was less than native enzyme of a similar activity level. All modified enzymes showed similar levels of improved shrink-resistance. (C) 2010 Elsevier Inc. All rights reserved.