The resistance of biological systems to the action of stress factors depends on the com-bined influence of the mechanisms that determine resistance through avoidance (reduction of the received dose) and the functional one, which influences the effectiveness of preventing and eliminating damage caused by stress. The relative contribution of the different mechanisms on the total resistance is variable depending on the specifics of the evolutionary adaptations of the species and on the transformations induced during the ontogenesis of the individual by environ-mental factors. It is important to note that the individual adaptations during ontogenesis involve changes in both mechanisms leading to increased resistance due to avoidance and functional adaptations. The level of resistance induced in ontogenesis depends on several factors, among which we mention the genetic characteristics of the organism, the dose, and specificity of the abiotic or/and biotic stress factor, the application of preparations that influence adaptation, pro-tection, and other processes induced in response to the action of the stress factor. Recently, a specific group was separated from plant growth regulators, called biostimulators. They include compositions of components, substances, and microorganisms, which, being applied to plants or soil, improve vigor, yield, quality, and resistance to environmental abiotic stress factors. In this presentation, we include some results that describe the biological effects of the biosti-mulator Reglalg. The obtained results suggest that the preparation activity is reflected in the plants’ resistance to abiotic and biotic stress factors. As in the case of growth stimulators and growth inhibitors, experimental data suggest that some mechanisms of action of biostimulators and plant protection preparations against biotic stress factors are congruent. Therefore their separation may lead to a decrease in the effectiveness of the practical use of both groups of preparations in agriculture.