Method for terminating peroxidase reaction, and terminating agent for said reaction

A method for terminating a peroxidase reaction, characterized by adding citric acid preferably at a final concentration of 0.125 M or more to a peroxidase reaction solution containing a peroxidase and a tetraalkylbenzidine or a salt thereof. According to the present invention, the sensitivity or accuracy of the measurement of the activity of a peroxidase can be improved and an effect of improving the safety of a reaction termination operation and a reaction-terminating agent can be achieved. Therefore, the present invention is useful in the fields of immunobiochemistry, genetic engineering, applied biological science and medicine.