The preferential interactions of lysozyme with solvent components and the effects of solvent additives on its stability were examined for several neutral osmolytes: L-proline, L-serine, gamma-aminobutyric acid, sarcosine, taurine, alpha-alanine, beta-alanine, glycine, betaine, and trimethylamine N-oxide. It was shown that all these substances stabilize the protein structure against thermal denaturation and (except for trimethylamine N-oxide for which interaction measurements could not be made) are strongly excluded from the protein domain, rendering unlikely their direct binding to proteins. On the other hand, valine, not known as an osmolyte, had no stabilizing effect, although it induced a large protein-preferential hydration. A possible explanation is given for the use of these substances as osmotic-pressure-regulating agents in organisms living under high osmotic pressure.