The physical properties of hen-egg-white lysozyme, and other globular protein, in aqueous solutions depend in a complicated and unexplained way on pH, salt type and salt concentration. One important and previously neglected source of ion specificity is the ionic dispersion potential that acts between each ion and the protein. We present model calculations, performed within a modified ion-specific double layer theory, that demonstrate the large effect of including these ionic dispersion potentials. (C) 2004 Elsevier Ltd. All rights reserved.