Nitrate uptake of Na(+) -deficient Amaranthus tricolor L. cv Tricolor seedlings from complete culture solution was stimulated by about 210% within 5 hours by application of 0.5 millimolar NaCl. From a Na(+) -preloading experiment, intracellular Na(+) was shown to be responsible for the stimulation of NO(3) (-) uptake. The results suggest a possible role of Na(+) in NO(3) (-) uptake in C(4) plants.