1. In the presence of cupric chloride, aryldiazonium chlorides arylate thiourea to give S-arylisothiuronium compounds. 2. In the absence of CuCl2, the reaction of the p-chlorophenyldiazonium fluoborate and chloride with thiourea gives the p-phenylenediisothiuronium compound, and the p-chlorophenylisothiuronium compound in the presence of CuCl2.