Hydrazine in water samples is determined by constant current chronopotentiometry in porous carbon electrodes. Hydrazine in alkaline solutions is oxidised to nitrogen in the pores of the electrode by constant current. Two types of electrodes made of reticulated vitreous carbon (RVC) were used, one fabricated from crushed RVC particles, the other with the original RVC material of 100 ppi porosity. The former is suitable for hydrazine concentrations above 0.7 mg·dm^-3 up to 50 mg·dm^-3, the latter for the 8-700 μg·dm^-3 range. The method was used for water samples, including boiler water.