Methylisothiazolinone-d3 (hydrochloride) is the deuterium labeled Methylisothiazolinone (hydrochloride). Methylisothiazolinone hydrochloride is the constituent of the biocide Kathon CG. Methylisothiazolinone hydrochloride is an isothiazolone derivative widely used as a preservative. Methylisothiazolinone hydrochloride is also a moderate sensitizer and reacts with GSH.