Feulgen stain can visualize DNA on tissue sections and in cells. This staining is the most used staining to highlight DNA in histology.

The principle of Feulgen stain is to dissociate the two strands of DNA through hydrolysis by a solution of molar HCl which destroys the purine bases. HCl separates the two purine bases of DNA: adenine, guanine, liberating the hemiacetal functions of deoxyriboses. This is to make accessible the deoxyriboses so that fuchsin (Schiff's reagent) can react with the aldehyde groups. The Schiff reagent then reacts with the reducing functions forming a red precipitate. So the DNA is colored in red rose. This staining is more or less intense depending on the degree of chromatin spiralization and is therefore particularly suitable for highlighting the chromosomes in the nucleus during mitosis. The pink stained bands that appear then correspond to the genes, and the light bands to the intergenic regions.