The synthesis of high-grade chloramine was studied starting from sodium hypochlorite solutions containing 25% in NaOCl. The reagents at 100 chlorometric degrees are relatively stable and lose approximately 1.4 degrees by 24h at 17 degreesC. They present a temperature of crystallization of 14.2 degreesC (precipitation of NaOCl . 5H(2)O) but it is possible to use them at - 20 degreesC in undercooling state. To obtain quantitative yields, it is necessary to neutralize the totality of hydroxide ions generated by the reaction and to operate below -10 degreesC in order to limit oxidation of chloramine by the hypochlorite ions. The addition of an acceptor soluble salt is the most appropriate solution because it regenerates ammonia as soon as it is consumed and stabilizes chloramine by maintaining the pH around 10. The ammoniacal combinations NH4NO3-NH4Cl-NH3-H2O and NH4NO3-NH3-H2O are compatible and allow to operate in monophasic medium until -30 degreesC. The yields are close to 95% with a titre in NH2Cl of 2.3 M (11.4%). Experiments carried out in continuous rating lead to a monochloramine solution of 2M.