Methylation of key biological molecules and proteins plays important roles in numerous biological systems, including signal transduction, biosynthesis, protein repair, gene silencing, and chromatin regulation. The SAM dependent MTs use SAM as the enzymatic cofactor. SAM, also known as AdoMet, acts as a donor of a methyl group that is required for the modification of proteins and DNA. Cayman’s MT Colorimetric Assay is a continuous enzyme-coupled assay that can continuously monitor SAM-dependent MT activities. The removal of the methyl group from SAM generates AdoHcy, which is rapidly converted to urate and H2O2 by an enzyme mixture provided in the kit. The rate of production of H2O2 is measured with the colorimetric reagent, 3,5-dichloro-2-hydroxybenzenesulfonic acid, by an increase in absorbance at 500-520 nm. The assay is supplied with AdoHcy as a positive control. The assay can be used with any purified SAM-dependent MT.