Several extracting solutions were evaluated for their effectiveness in determining NO3- potentiometrically with a selective nitrate ion electrode, and the results were compared with a standard phenoldisulfonic acid method. The nitrate electrode proved to be highly satisfactory for determining NO3- in plant tissue, and is apparently as accurate as the phenoldisulfonic acid method when Al2(SO4)3 +10 mg per ml NO3-N is the extracting solution.