Simultaneous measurements of minute electrical current and water flow through single living cells of Nitella translucens have shown that there is an electro-osmotic transport of the order of 100 moles of water per Faraday in the direction of the positive ion flow. This implies the existence of water-filled charged pores through the plasmalemma and tonoplast of the Nitella cell. The pores available for ion movement are far too few to account for the high water permeability of the cell membranes, and the possible extra turgor pressures which might be produced by an electro-osmotic flow through these pores could not be more than 10−4 atmosphere.