Histone acetyltransferases (HATs) are involved in the regulation of gene transcription in eukaryotic cells and their inhibitors could be a promising class of drugs due to their ability to modulate transcription and exert antiviral, anti-inflammatory as well as antioxidant effects. Nonradioactive spectrophotometric HAT assay is an alternative method to the widespread radioactive assay but suffers from drawbacks as lack of sensitivity and accuracy. A simple, non-radioactive fluorescent assay that measures the production of CoASH was established by its facile reaction with O-phthalaldehyde and 2-amino-ethanol. This method gives much higher accuracy compared to spectrophotometric assay, and allows screening of various compounds with potential HAT inhibition. The novel assay should be a valuable tool in transcriptional research and especially drug discovery.