Synthesised organic compounds of pyrimidinecarboxylic acids are characterised by high biological activity, even when their concentrations are low. These compounds, when applied to the seeds of Rhododendron, a genus of woody plants, with concentrations of 0.01, 0.05, and 0.1 %, stimulate the growth of the plants. The effect is more obvious 3 months after the start of the experiment, rather than 7 months after. Thus, Rhododendron ledebourii Pojark. seedlings grew by 13.3-33.5 %, and Rhododendron smirnowii Trautv. seedlings grew by 29.6-48.1 %. Rhododendron ledebourii and Rhododendron smirnowii seedlings demonstrated similar direct correlations: when the concentration of 2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid and 4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid (for Rhododendron ledebourii seeds only) rose from 0.01 to 0.1 %, the height of the seedlings increased. It is suggested using 4-methyl-2-piperidin-1-yl-pyrimidine-5-carboxylic acid, 2-benzylamino-4-methyl-pyrimidine-5-carboxylic acid, and 4-methyl-2-morpholin-4-pyrimidine-5-carboxylic acid at concentrations of 0.01, 0.05, and 0.1 % as growth stimulants for the species of Rhododendron genus.