Chaperones have an important role in the repair of proteotoxic damage, which is greatly increased in aged subjects. Chaperone levels and expression were subject of numerous studies in aged organisms. However, there were only very few attempts to measure chaperone activity in aged animals. Here, we report our initial studies showing a decreased chaperone capacity of liver cytosol from aged rats compared to those of young counterparts. The amount of Hsc70/Hsp70 was not significantly different in livers of young and aged rats. On the contrary, old animals showed a significant decrease in their hepatic Hsp90 content, which may explain their decreased chaperone activity. The observed decrease in chaperone capacity may also reflect a direct proteotoxic damage of chaperones, or an increase in chaperone occupancy, i.e. a 'chaperone overload' due to the increased amount of damaged hepatic proteins in aged rats. Experiments are in progress to elucidate the mechanism of the observed age-induced changes in chaperone function.