Abstract
The naphthol, M-nadi and benzidine reactions of myeloid elements show a number of differential features which indicate that their mechanisms are not identical. The naphthol reaction probably depends on the binding of some naphtholic polymer by an unidentified substrate, resulting in lipid-like staining properties and phenolic functions. The mechanism of the M-nadi reaction is not clear. The benzidine reaction is contingent on a peroxidase-like effect; whether enzymatic or not, cannot be determined on the basis of data available.