Histone deacetylases (HDACs) represent a large family of enzymes identified as key regulators of nucleosomal histone acetylation, a major event that controls eukaryotic gene transcription and are classified into three groups. They are believed to be involved in important biological activities, such as cell differentiation, proliferation, apoptosis, and senescence. In the PromoKine HDAC-3 Inhibitor screening Kit, HDAC-3 and developer will deacetylate and cleave the substrate [Arg-His-Lys-Lys(Ac)-AFC] to release the AFC molecule, which can be detected by fluorometric method (Ex/Em = 380/500 nm). In presence of a HDAC-3 inhibitor, the cleavage will be inhibited. The kit provides a rapid, simple, sensitive, and reliable test, which is also suitable for high throughput screening of HDAC-3 inhibitors. Trichostatin A (TSA) is included as a control inhibitor to compare the efficacy of the test inhibitors.