4,5-Dimethyl-o-phenylenediamine-d8 is the labelled analog of 4,5-Dimethyl-o-phenylenediamine. 4,5-Dimethyl-o-phenylenediamine is used in biological processes as a substrate for CobT nicotinate-mononucleotide:5,6-dimethylbenzimidazole phosphoribosyltransferase from Salmonella typhimurium LT2.