A Simple Azo-Dye Method for Histochemical Demonstration of Acid Phosphatase

A NEW diazonium salt, ‘hexazonium pararosanilin’, introduced for simultaneous azocoupling methods by Davis and Ornstein1, was successfully employed in the demonstration of esterases at microscopic and electron-microscopic levels2,3. It was found that a method using α-naphthyl phosphate and hexazonium pararosanilin as coupler gives far better localization of acid phosphatase than any other method4 using the same substrate, and the results seem to be not inferior to techniques using ‘Naphthol AS’5 or indoxyl phosphates6. The advantages of this method, besides the very good localization, are that α-naphthyl phosphate is water-soluble; it is more readily hydrolysed than the phosphate esters of ‘Naphthol AS’, or indoxyl derivatives, the reagents are commercially available, and the method works easily.