Plants develop various mechanisms to adapt to nutrient availability. When nitrate (NO₃^-) is supplied locally to nitrogen-deficient plant roots, the growth of lateral roots (LRs) located on that part of root is stimulated. It is unclear if an auxin signalling pathway is involved in this process. By using a 3-segment agar culture system, the role of auxin in the above situation was investigated by supplying 1-naphthalene acetic acid (NAA), 2,3,5-triiodobenzoic acid (TIBA) and 6-benzylaminopurin (6-BA) exogenously to two maize inbred lines (478 and Wu312) in which lateral roots show a differential growth in response to a local nitrate supply. In 478, LR growth was stimulated by local NO₃^- at concentration from 0.25 to 25 mmol L^-1 NO₃^-. In Wu312, the effect of local NO₃^- was only significant at concentration at 1 mmol L^-1 NO₃^- and this positive effect disappeared when NO₃^- concentration exceeded 5 mmol L^-1. The inefficient response of LRs at low (0.5 mmol L^-1) and high (7.5 mmol L^-1) local NO₃^- in Wu312 could be restored to the same maximum level as at 1 mmol L^-1 NO₃ ^- by exogenously application of NAA. When TIBA, the auxin transport inhibitor, was supplied in the upper, or middle segments where local NO ₃^- was added, to stop shoot-to-root auxin transport, the stimulatory effect of local NO₃^- was completely eliminated. When TIBA was supplied at the lower segment to stop basipetal auxin transport from root tip to lateral root meristem, the stimulatory effect of local NO₃^- supply was not affected. Exogenous supply of cytokinin 6-BA, the antagonist hormone to auxin also completely eliminated the stimulatory effect of local NO₃^- supply. It was concluded that the stimulation effect of local nitrate on lateral root growth depends on auxin transport from shoot to root. Auxin transport from the root tip basipetal to the lateral root meristem is of less importance for this response. A differential response among different genotypes is a real possibility, and this difference might be due to their differential sensitivity to auxin.