In the presence of hydroxylamine, the catalytic wave of ruthenium (Ⅲ) appears at -0.6 to 0.7 V (S.C.E.) (depending on the composition of the solution) in Britton-Robinson buffer solution. The polarographic behaviour of this catalytic wave is studied by means of the dependence of the wave behaviour on the composition of the polaro-graphic solution and on the height of the mercury reservoir, the time beater, the temperature dependence, etc.