Aim. To study the effect of polymeric biocide polyhexamethylene guanidine hydrochloride (PHMG-Cl) on morphophysiological and biochemical parameters of wheat seedlings in the presence of toxic concentration of copper ions. Methods. The growth-stimulating activity of PHMG-Cl in pure state, as well as in the presence of elevated concentrations of copper ions was studied by phytotesting method using wheat seed as a test culture. Physico-chemical interaction between PHMG-Cl and CuSO4 in water solutions was studied by spectrophotometry. Results. Wheat seed treatment with water solutions of polymeric biocide PHMG-Cl in the concentration range of 0.01–0.1 % causes an increase in the length of roots and shoots by over 50 % after 7 days of incubation. The concentration of PHMG-Cl of 1 % was found to have a depressive effect on growth characteristics of the tested plants. This fact indicates that the phytotoxicity of PHMG-Cl is at least two orders of magnitude lower compared with a common pesticide copper sulfate. Thus, wheat seed soaking in 200 μM (0.003 %) water solution of copper sulfate causes reduced length of shoots and roots (by 65 and 34 %, respectively), as well as reduced weight of shoots (by 20 %) and roots (by 74 %) The analysis of green mass showed signifi cantly reduced content of carotenoids (by 26 %) and water soluble fl avonoids (by 37 %), as well as chlorophyll a/b ratio (by 18 %) that indicates decreased plant metabolic activity. However, the toxic effect of copper sulfate ions signifi cantly diminished in the presence of PHMG-Cl (0.01 %). Thus, the length of shoots and roots was found to increase by 24 and 64 %, respectively, compared to the samples treated with CuSO4. Moreover, the content of pigments and fl avonoids in the green mass of seedlings reached the level of control samples. The results of spectrophotometric studies indicate the absence of physico-chemical interaction between PHMG-Cl and copper sulfate in water solutions. Conclusions. The polymeric biocide PHMG-Cl effectively stimulates growth and development of wheat seedlings in the concentration range of its water solutions of 0.01–0.1 %. In the presence of toxic copper sulfate concentration, PHMG-Cl does not possess the growth stimulating activity. However, the polymeric biocide signifi cantly improves copper stress resistance of plants, and normalizes their morpho-physiological indicators, photosynthetic characteristics and secondary exchange.