A procedure has been developed for the synthesis of substituted 2-methyiquinolin-4-yithiuronium salts by reaction of 2-methyl-4-chloroquinoline with N-substituted thioureas. Alkaline hydrolysis of these salts yields 2-methyl-4-quinolyl isothiocyanate instead of the expected 2-methylquinoline-4-thiol.