Phosphate, sulphate and chloride addition to lysozyme dissolved in pure water demonstrates three concentration-dependent stages for the thermal stabilization of the protein measured by differential scanning calorimetry. A three-stage model is proposed to explain this phenomenon.1 The first stage is direct interaction of the anions with charged side chains. This has an effect on lysozyme stability unrelated to the Hofmeister series.2 The second stage is direct interaction of the anions with partial charges on the protein’s surface and has a weak negative effect on lysozyme stability. The third stage is competition for water between the ions and the protein as it unfolds. This stabilizes the lysozyme structure. There is a clear transition between the second and third stage, in the case of sodium chloride, disodium sulphate and disodium hydrogen phosphate this is at 550 mM, 210 mM and 120 mM, respectively. At low ion concentrations the protein’s hydration layer is at equilibrium with the bulk water. After the transition bulk water is depleted and the protein is competing for water with the ions. This increases the free energy required to hydrate the interior of the protein as it unfolds and it is this that stabilizes the protein structure.