A new and accurate method for the determination of nitrate in sea water, based on the pola.rographic reduction of nitrate in the presence of uranyl ions, is presented. Sulfate ions depress the reduction current by a definite proportion, depending on the chlorinity of the water sample; for chlorinities in the range of 14 to 19 ‰, this effect is rather constant. Fluoride interferes strongly with the reduction of nitrate, but aluminum or zirconyl salts may satisfactorily eliminate this effect. Other interfering ions and preservatives are also discussed. A procedure for the determination of nitrate in sea water ha.s been proposed and its validity tested.