Techniques have been developed for continuous recording of electrical potential difference in maize root preparations. In this way the continuous p.d. profile along the lateral axis of the root could be obtained. The features of the profile are resolved in terms of the root morphology. Analysis of the p.d. profile indicates (a) that the phases within the root are electrically negative with respect to the bathing medium, (b) that the vacuoles are positive relative to the cytoplasm, i.e. a p.d. exists across the tonoplast, (c) that all cytoplasmic phases are equipotential, which indicates a continuity within and between the cortical and stelar symplasms, (d) that the extracellular space of the root is presumably only slightly influenced by the concentration of the external medium since the p.d. profile within the root does not react to changes of concentration in the external medium, (e) that the potential of the stelar vacuoles is negative relative to the cortical one and this is consistent with the accumulation of surplus ions in the stelar vacuoles. The implications of the present findings to the elucidation of ion transport mechanism across the root are briefly discussed.