Sodium thiosulfate 0.25% is a solution that occupies an important place in histology and in vitro diagnostics due to its chemical properties and composition, including sodium thiosulfate 5-hydrate and deionized water. In this regard, it can be used in various applications. Its function in histology should be emphasized, especially in the removal of mercury dichloride residues from tissue sections that have been fixed in mercury-containing fixatives. Here, the sodium thiosulfate reacts with mercury to form insoluble mercury compounds, which can then be easily washed out of the tissue. This chemical reaction allows for improved quality of histological staining and an increase in the detectability of fine tissue details. In scientific laboratories, the solution can also play an important role by serving as a reducing agent in various chemical reactions.