It is primarily used as a pH indicator (red below pH 4.4 yellow above pH 6.2) in microbiology for Methyl Red-Voges Proskauer (MR-VP) tests to detect mixed acid fermentation and in analytical titrations.

Its main purpose is to undergo reversible protonation of the azo and dimethylamino groups producing sharp color changes for endpoint detection in weak base-strong acid titrations and bacterial glucose metabolism identification.

Methyl red (CHNO) is a dark red to purple crystalline powder azo dye featuring two aromatic rings connected by an NN azo linkage with a dimethylamino group on one ring and a carboxylic acid on the ortho position of the other molecular weight 269.30 gmol and melting point 178-182 C.