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. HDACs are transcriptional repressors with crucial roles in mammalian development. They are believed to be involved in important biological activities, such as cell differentiation, proliferation, apoptosis, and senescence. In the PromoKine HDAC-3 Activity Assay Kit, HDAC-3 and Developer will deacetylate and cleave the substrate [R-H-K-K(Ac)-AFC] to release the AFC molecule, which can be detected fluorometrically (Ex/Em = 380/500 nm). The kit provides a rapid, simple, sensitive, and reliable test, which is also suitable for high throughput measurement of HDAC-3 activity in purified, immunoprecipitated and recombinant or genetically modified HDAC-3 samples.