A group of naphthols—1- and 2-naphthol, 6-benzoyl-2-naphthol and 6-bromo-2-naphthol—have been investigated in relation to their tissue affinity. It has been found that naphthol binding is mainly dependent on the solubility of the naphthols and on the type of tissue considered. Time of incubation, naphthol concentration and pH also play in important role in the intensity of the resulting stain. 1- and 2-naphthol have very little affinity for cell constituents, while 6-bromo-2-naphthol and 6-benzoyl-2-naphthol are strongly bound by cellular structures. The affinity of the latter two naphthols is specific for cell parts and tissue type: the cytoplasm of epithelial cells is strongly stained, while connective tissue, kidney glomeruli and inner medulla and cell nuclei at the concentration used devoid of any naphthol binding. Correlated experiments have been carried on the histochemical demonstration of enzymes utilizing the esters of these naphthols, by simultaneous and post-incubation coupling methods. Considerations have been offered on the importance of specific tissue and cellular affinity of insoluble naphthols in relation to the reliability of histochemical localization of enzymes by the post-incubation coupling technique.