Recently, we have shown that ethylene-glycol, a co-solvent commonly used in studying protein folding, strongly affects the dielectric response of lysozyme. The data were coherently interpreted hypothesizing that glycol molecules wedges between and separates the two domains of lysozyme making them rotationally independent. In this Letter, we describe a new dielectric experiment on lysozyme in water/ethylene-glycol solutions in the presence of N-acetyl-D-glucosammine, a well known inhibitor for the protein. The results indicate that the interaction of ethylene-glycol with the protein is markedly influenced by NAG, in the sense that the saccharide preferentially links with lysozyme driving away the glycol molecules. (C) 2004 Elsevier B.V. All rights reserved.