Methylene blue 5% aqueous is a staining solution containing 5% methylene blue in water. Methylene blue is a commonly used stain in microbiology and histology that binds to acidic cellular components and stains them blue.

The 5% aqueous methylene blue solution is used in a variety of applications, including the staining of bacteria, fungi, and protozoa in microbiology, and the staining of cell nuclei and cellular structures in tissue sections in histology. Methylene blue can also be used as a component of staining solutions in combination with other dyes to visualize different cell structures and tissue components simultaneously.

In cell biology, the 5% aqueous methylene blue solution is also used as a reducing agent for the reduction of metachromasia. This solution is easy to prepare and use, and it can be diluted or modified for different applications, depending on the specific requirements of the experiment or study.