Abstract: An oxidative chromogenic reagent free from interference by bilirubin used for the measurement of a biogenic substance by an enzymatic analysis, which comprises a compound or a salt thereof represented by the following formula wherein R.sup.1 and R.sup.2 independently represent a C.sub.3-4 -alkly group substituted with a sulfonic acid group or a C.sub.3-4 -hydroxyalkyl group substituted with a sulfonic acid group; and R.sup.3 and R.sup.4 independently represent a C.sub.1-4 -alkyl group, a C.sub.1-4 -alkoxy group, a substituted or non-substituted carbamoyl group, an acyl-substituted amino group, an aryl group, or a halogen atom. The reagent is stable and has excellent water solubility, and it enables high sensitive and accurate measurement because interference by bilirubin is substantially reduced or eliminated.