High-pressure SANS experiments have been performed on acidic dilute solutions of the dimeric protein P-lactoglobulin. To evidence the solvent effect on the protein stability during compression, two different solvents, D2O and a 50% w/w mixture of water and ethyleneglycol have been considered. Data confirm that pressure induces dissociation in both solvents, even if P-lactoglobulin shows an higher stability in 50% ethylene-glycol. An original global fitting procedure has been used to derive the thermodynamic parameters that describe the dissociation equilibrium. As a result, the role of the solvent in protein dissociation has been observed to reflect on volume and compressibility changes. (c) 2005 Elsevier B.V. All rights reserved.