Summary: The HDAC Colorimetric Assay/Drug Discovery Kit is a complete assay system designed to measure histone deacetylase (HDAC) activity in cell or nuclear extracts, immunoprecipitates or purified enzymes. It comes in a convenient 96-well format, with all reagents necessary for Colorimetric HDAC activity measurements and calibration of the assay. In addition, a HeLa nuclear extract, rich in HDAC activity, is included with the kit. The extract is useful as either a positive control or as the source of HDAC activity for inhibitor/drug screening. Also included is the potent HDAC inhibitor, Trichostatin A, which may be used as model inhibitor.