Measurements of the difference in electropotential between the interior of the cell and the external solution have been made for the first time in cells of several crop plants (1). The interiors of cells of Avena, Pisum, and Zea seedling tissues all have potentials of about -80 to -115 mv relative to that of an external solution of 0.1 mmole of KCl per liter, bathing the tissue. The potential difference of Avena coleoptiles varies with the concentration of external KCl and is depressed by 2,4-dinitrophenol. The potential difference occurs between the cytoplasmic layer and the exterior; the potential of the vacuole does not appear to be significantly different from that of the cytoplasm. Obviously a relatively large cation accumulation ratio could be accounted for in plant cells by this large potential without invoking a chemical cation transport scheme.