The ATP-ubiquitin-dependent pathway in eukaryotes is a complex system, which plays an essential role in selective protein degradation. The functional diversity of this system must be matched to the specific protein metabolism related to the physiology of each cell types. The aim of our work was to study the expression of different components of the proteasome-dependent pathway in various rat tissues. Therefore we quantified the 20S proteasome and the 19S and 11S regulators by Western blot, and measured the expression of the mRNAs of certain subunits, which are markers of these components. We compared the peptidase activities of the purified 20S proteasomes, and also mapped its components by 2D electrophoresis. Our results show that the components of the ATP-ubiquitin-dependent pathway vary considerably both in abundance and activity from one tissue to another. This diversity allows the cells to respond appropriately to tissue-specific protein metabolism in the rat.