Esterases are ubiquitous in nature and encompass a series of different enzymes acting upon select substrates. According to the methodology, α-naphthyl acetate is enzymatically hydrolyzed, liberating a free naphthol compound. This then couples with a diazonium compound, forming black colored deposits at sites of non-specific esterase activity. This enzyme is detected primarily in monocytes, macrophages and histocytes, and is normally absent in granulocytes. Lymphocytes may occasionally exhibit enzyme activity. A sodium fluoride inhibition procedure may be run to demonstrate monocyte inhibition. The procedure is run at 37 °C and may be utilized with blood, bone marrow films, tissue-touch preparations, cytocentrifuge preparations and frozen sections. The enzyme does not survive paraffin processing.

Intended for the cytologic demonstration of a-naphthyl acetate esterase in blood, bone marrow films or tissue touch preparations.