Preferential interactions between proteins and metals play an important role in a great number of physiological and biochemical processes. With these premises, the inÑuence of LiCl on the conformation and function of lysozyme has been the main object of our studies. Viscometric, densimetric, solubility and spectrophotometric measurements were carried out. The results revealed that lysozyme can undergo a weak conformational transition due to the preferential interaction between salt and protein. The lysozyme takes on a more packed conformation than when in water solution, which is related to the preferential binding of salt inside the protein structure, at salt concentrations below 0É7 M LiCl. A total salt exclusion from the lysozyme internal domain was observed at salt concentrations above 0É7 M LiCl. A salting-in behaviour was exhibited at salt concentrations below 0É7 M LiCl, while a signiÐcant salting-out behaviour above this salt concentration was shown. The thermodynamic stability of the system is higher at large salt amounts in the medium. There is no direct interaction of the salt with the active site of the enzyme and LiCl manifests a non-competitive inhibitor character for lysozyme, at every salt concentration studied.