Grocott's stain is used in histology for the visualization of fungi, certain pathogens, basement membranes, and histologic structures in general.

The Grocott stain procedure begins with the use of a periodic acid solution to oxidize 1,2-glycols to aldehydes. During the incubation with the methenamine - silver - borate solution, the aldehydes are reduced and at the same time cause the reduction of ferric ions to metallic silver. This is manifested by the presence of black deposits on the tissue section.

This is followed by toning the solution with gold chloride solution which further enhances the staining intensity of target structures (fungi, basement membranes and others), and reduces background staining.

Excessive unrelated silver-gold bonds are removed by rinsing the section with sodium thiosulfate solution. Finally, the sections are exposed to the Fast Green FCF dye that colors the background structures; this in turn creates a clear and visual contrast with the target structures (colored in black).

Here are the examples of colorations obtained with the Grocott stain: