A number of naturally occurring small organic molecules, primarily involved in maintaining osmotic pressure in the cell, display chaperone-like activity, stabilizing the native conformation of proteins, and protecting them from various kinds of stress. Most of them are sugars, polyols, amino acids or methylamines. Similar to molecular chaperones, most of these compounds have no substrate specificity, but some specifically stabilize certain proteins. In the present work, the capacity of trehalose and glycerol, two well-known osmolytes, to stabilize and renature inorganic pyrophosphatase is demonstrated. Both trehalose and glycerol significantly protect pyrophosphatase against thermoinactivation achieved by incubating the enzyme at temperatures up to 95 degrees C, and allow the enzyme already inactivated in the presence of these osmolytes to renature upon incubation at low temperatures. To the best of our knowledge, there are no data on the effects of these compounds on renaturation of thermoinactivated proteins. The correlation between the recovery of enzyme activity and structural changes indicated by fluorescence spectroscopy contribute to better understanding of the protein stabilization mechanism.