The proteasome is a multicatalytic proteinase complex that is involved in the selective degradation of intracellular proteins. The 20S proteasome is the proteolytic core particle of a large protein degradation complex, the 26S proteasome. Proteasome inhibitors exhibit anti-inflammatory and antiproliferative effects, evidence that the proteasome may be an important drug target for the treatment for cancer and inflammatory diseases. Cayman's 20S Proteasome Assay Kit employs a specific 20S substrate, SUC-LLVY-AMC which, upon cleavage by the active enzyme, generates a highly fluorescent product with an emission wavelength at 480 nm. The kit is easy to use and can be easily adapted to high-throughput screening for therapeutic compounds regulating activation of the 20S proteasome.