Abstract <p>Enzymatic inhibitory assay based on the coupled enzyme system NAD(P)·H:FMN oxidoreductase and luciferase (Red + Luc), originally developed for environmental monitoring of soils, water, and air, is proposed as a method for evaluating changes in the properties of active ingredients of pesticide preparations depending on the additional components (formulants), as well as when pesticides are combined in mixtures. Using the commercial pesticide preparations containing glyphosate, it was shown that the degree of inhibition of the coupled enzyme system Red + Luc largely depends on the formulants rather than on the active ingredient in their composition. Moreover, the combined inhibitory effect of the pesticides mixture on the coupled enzyme system Red + Luc was not additive. According to the results of the inhibitory assay, the type of interaction of pesticide preparations in mixtures depends on both the formulants used and the ratio of pesticides in the mixture.</p>