A simple method is proposed for the synthesis of 1,2,3-thiadiazolylureas by the reaction of 1,2,3-thia-diazolyl isocyanates with primary amines. 1,2,3-Thiadiazolyl isocyanates were obtained in situ by the Curtius rearrangement of 1,2,3-thiadiazolylcarbonyl azides. Cytokinin activity was tested for N-(4-methyl-1,2,3-thiadiazol-5-yl)-N'-(4-methylphenyl)urea, which is an analog of thidiazuron, differing in the presence of two methyl groups in the molecule.