[Tetramethylbenzidine--a chromogenic substrate for peroxidase in enzyme immunoassay]

3,3' 5,5'-tetramethylbenzidine (TMB) is a high sensitive chromogenic substrate for horseradish-peroxidase as a marker enzyme. In an enzyme immunoassay (EIA) for alpha-1-fetoprotein and in an rapid EIA for myoglobin it reveals higher sensitivity compared to o-phenylenediamine, the increase depends on reaction time. The optimal peroxide concentration depends on reaction time of enzyme chosen in different assays. TMB used for histochemistry is also suitable for EIA if hydrochloric acid is used as stopping reagent. TMB lacks in mutagenic properties and it should preferred for peroxidase rather than all other chromogenic substrates applied up to now.