Dimethyl sulfate (DMS) is a diester of methanol and sulfurous acid. Dimethyl sulfate is a potential reagent for the methylation. It is a substrate for sulfite oxidase. Dimethyl sulfate is stable in blood and can be transported from the intestines to the alveoli and the air. Therefore, DMS in the blood is accepted as a marker of halitosis. The high DMS levels in systemic circulation detected in the multicenter case-control clinical study of laryngopharyngeal reflux.