In the histochemical staining of enzymes by the chelate removal method, the substrate is a chelate, and the enzyme unmasks bound ions which are precipitated by suitable capturing ions in the incubating mixture. The new method allows the staining of phosphatases which act on substrates that are insoluble in the Gomori mixtures. Three inorganic polyphosphatases were stained in the first application of the chelate-removal principle: neutral triphosphatase, alkaline triphosphatase, and alkaline pyrophosphatase. The incubating media had lead-polyphosphate chelates as substrates, with "tris" or barbital buffers. Orthophosphate was added to some solutions as an auxiliary capturing anion. Alkaline triphosphatase as well as alkaline pyrophosphatase was demonstrated in the columnar epithelium of duodenal mucosa of mouse and rat, alkaline triphosphatase in the convoluted tubules of kidney, and neutral triphosphatase in bile canaliculi of liver. The properties of the three enzymes were examined, and the relation of the stains to biochemically defined enzymes of the inorganic polyphosphatase group was discussed. The chelate removal method was also used for the histochemical demonstration of adenosine tri- and diphosphatase. Evidence for this mechanism of ATP-ase staining is presented as an addendum.