Аннотация:Highly sensitive and selective methods for the determination of biologically active metals, especially such toxic ones as mercury, are becoming more and more important now because of the urgency of the problem of environmental protection. The use of enzymes is promising for the development of methods. In this case, it is necessary to keep in mind that the enzyme must be sufficiently stable, available (i.e., a commercial preparation), and relatively cheap for wide implementation of the method in analytical practice. Such an enzyme is horseradish peroxidase. In the present paper, we show the suitability and promise of using peroxidase to determine trace amounts of mercury.