Phosphotungstic acid-phosphomolybdic acid solution is mainly used in scientific laboratories, especially in histology and cytology for staining tissue samples to make certain cell structures more visible under the microscope. It consists of phosphotungstic acid and phosphomolybdic acid dissolved in distilled water. These acids react chemically with certain cellular components and lead to the formation of color complexes that allow the visual differentiation of cellular components. The solution has strong oxidizing and complexing capabilities due to the combination of the chemical properties of phosphotungstic acid (H3[P(W3O10)4]) and phosphomolybdic acid (H3[PMo12O40]). These properties are essential for the production of color complexes, which allow a differentiated view of biological material under the microscope. The reactions in the solution lead to the attachment of the complex molecules to specific tissue structures, depending on their chemical nature. The colour differentiations that can be achieved by using the solution typically include the highlighting of cellular structures such as nuclei, cytoplasm or specific inclusions, which supports the diagnosis and study of biological samples. Application in histology and cytology.