Azinobis(3-ethylbenzthiazoline-6-sulfonic acid)·2NH4-salt, abbreviated ABTS, is a chromogen for peroxidase in enzyme-linked immunoassay (ELISA) (1). ABTS is a substrate and for laccase and angiotensin I-converting enzyme assay (2). A peroxidase reaction of ABTS in the presence of hydrogen peroxide produces a green soluble end product which can be read spectrophotometrically at 405 nm. The reaction may be stopped with 1 % sodium dodecyl sulfate (SDS). Azinobis(3-ethylbenzthiazoline-6-sulfonic acid)·2NH4-salt, abbreviated ABTS, is a chromogen for peroxidase in enzyme-linked immunoassay (ELISA) (1). ABTS is a substrate and for laccase and angiotensin I-converting enzyme assay (2). A peroxidase reaction of ABTS in the presence of hydrogen peroxide produces a green soluble end product which can be read spectrophotometrically at 405 nm. The reaction may be stopped with 1 % sodium dodecyl sulfate (SDS).