Nitrate uptake by 9-day old maize seedlings and the potential difference (PD) along the root were studied in response to different accompanying cations (K + , Na + , Ca 2 + , Mg 2 + ). A computer-based system was used to measure the depletion of ions from the uptake solution. Stimulation of NO 3 - uptake by cations followed the sequence K + >>Mg 2 + >Na + ≥Ca 2 + . A positive correlation between NO 3 - and cation uptake rates was observed. The uptake rate analysis indicated higher a V m a x value but the same K m for nitrate uptake from solutions with K + compared with solutions with Na + , Mg 2 + , Ca 2 + . Treatment of nitrate-induced maize roots with KNO 3 caused a rapid and steady decrease in PD value. The electrical response of roots to NaNO 3 , Ca(NO 3 ) 2 and Mg(NO 3 ) 2 was characterized by initial rapid decreasing of PD followed by a slower increasing of PD. The pattern and magnitude of the electrical response were dependent both on ion concentration and the resting potential. The importance of the cation-dependent membrane potential changes in regulation of nett nitrate uptake is discussed.