This work is devoted to the screening for new effective plant growth regulators based on synthetic compounds, pyrimidine and pyridine derivatives. Study of the plant growth-regulating activity of synthetic compounds was carried out on spring barley (Hordeum vulgare L.) variety Avatar. The effect of synthetic compounds on the morphometric parameters of barley plants grown in laboratory conditions was studied. The plant growth-regulating activity of synthetic compounds was compared with the plant growth-regulating activity of phytohormones auxins IAA (1H-indol-3-yl)acetic acid) and NAA (1-naphthylacetic acid). The most biologically active synthetic compounds were selected, which show plant growth-regulating activity, similar to or exceeding the activity of auxins IAA and NAA. The highest parameters of the average length of the shoots, which exceeded similar parameters of control plants by 13.73 - 24.06 %, were obtained on 2-week-old barley plants treated with synthetic compounds, derivatives of sodium and potassium salts of 6-methyl-2-mercapto-4-hydroxypyrimidine (Methyur and Kamethur), 6-methyl-2-propylsulfanyl-pyrimidin-4-ol, 2-benzylsulfanyl-6-methylpyrimidin-4-ol, and sodium 4-hydroxypyrimidine--2-thiolate, respectively. The highest parameters of the average length of the roots, which exceeded similar parameters of control plants by 66.67 – 121.35 %, were obtained on 2-week-old barley plants treated with synthetic compounds, derivatives of N-oxide-2,6-dimethylpyridine (Ivin), sodium and potassium salts of 6-methyl-2-mercapto-4-hydroxypyrimidine (Methyur and Kamethur), 2-ethylsulfanyl-6-methylpyrimidin-4-ol, and 6- methyl-2-propylsulfanyl-pyrimidin-4-ol, respectively. The highest parameters of the average biomass of 10 plants, which exceeded similar parameters of control plants by 30.59 – 86.46 %, were obtained on 2-week-old barley plants treated with synthetic compounds, derivatives of N-oxide-2,6-dimethylpyridine (Ivin), sodium and potassium salts of 6-methyl-2-mercapto-4-hydroxypyrimidine (Methyur and Kamethur), 6-methyl-2-propylsulfanylpyrimidin-4-ol, and sodium 4-hydroxypyrimidine--2-thiolate, respectively. A comparative analysis of the growthregulating activity of auxins showed that the morphometric parameters obtained on 2-week-old barley plants treated with IAA and NAA, exceeded similar parameters of control plants, as follows: plant shoot length by – 7.51 - 20.57 %, plant root length – by 15.45-32.81 %, plant biomass – by 39.59 – 49.01 %, respectively. It was shown that pyrimidine and pyridine derivatives at a concentration of 10-7M exhibit cytokinin-like activity in increasing the content of photosynthetic pigments in the leaves of barley plants. The content of chlorophyll a increased by 6.46 - 68.33%, chlorophyll b increased by 6.2 - 64.11%, chlorophyll a+b increased by 6.37 - 66.81%, carotenoids increased by 2.65 - 29.81%, respectively, compared with similar parameters of control barley plants treated with distilled water. The practical use of the synthetic compounds, pyrimidine and pyridine derivatives: Methyur, Kamethur, Ivin, and other selected most active synthetic compounds for improving the development of shoots and roots, increasing the biomass of spring barley (Hordeum vulgare L.) variety Avatar in the vegetative phase, and increasing the content of photosynthetic pigments in plant leaves is proposed.