In the preparation of a 2-arylamino-4,6-dichloro-s-triazine of the formula ##STR1## in which R.sup.1 is an optionally substituted aryl radical, andR.sup.2 is hydrogen or alkyl,by reacting cyanuric chloride of the formula ##STR2## with a virtually water-insoluble arylamine of the formula ##STR3## at a temperature between 0.degree. and 100.degree. C., the improvement which comprises effecting the reaction in water at an acid pH in the presence of a virtually water-insoluble organic solvent. The resulting aqueous phase contains the triazine in such high purity and concentration that it can be used without further purification. The organic solvent can be recycled.