Naphthol AS-D , 3-Hydroxy-2-naphtho-toluidide; C.I. 37520

Naphthol AS-D is a diagnostic chemical for phosphatase enzymes and is used to stain cells, tissues, and body fluids for diagnosis. The chemical reacts with the amino groups of proteins in cells and produces a brown color. Naphthol AS-D is not toxic to living cells in concentrations below 5%. It stains basophilic leukemia cells as well as brain cells. This chemical can be used to diagnose cutaneous lesions, such as psoriasis or melanoma, which are difficult to diagnose by standard methods.  present in these lesions and produce a brown color.