Root growth is important for the acquisition of nitrogen (N) and water in deep sandy soil profiles with high leaching potential. Root growth characteristics and the N uptake of wheat genotypes differing in early vigour were investigated in 2 glasshouse experiments. In both experiments the vigorous breeding lines Vigor18 and B18 and the well-adapted commercial cultivar Janz were grown in glass-walled growth boxes in a controlled-temperature glasshouse up to the onset of stem elongation. In Expt 1, rooting parameters and detailed measurements of root growth and proliferation were made at 2-day intervals using a root mapping technique. In Expt 2 the glass-walled growth boxes were segmented into upper (0-0.2 m), middle (0.2-0.7 m), and bottom (0.7-1.0 m) soil layers, and the contribution of N fertiliser uptake by roots from each soil layer to the total plant N uptake was determined by applying 15N-urea to a single soil layer each time. The accumulated total root length across the soil profile from the 1-leaf stage to the onset of stem elongation was 33-83% higher in the vigorous lines Vigor18 and B18 than in Janz. The roots of the 3 genotypes grew vertically down the soil profile at a similar rate, but the roots of vigorous lines branched earlier and grew horizontally faster and more extensively than those of cv. Janz, resulting in a greater root-length density and root number in the top 0.7-m soil layer. Uptake of N fertiliser by roots in the upper 0-0.2 m of the soil profile was 60-68% higher in the vigorous lines than in Janz. Roots of the vigorous lines located in the segment 0.2-0.7 m of the soil profile captured twice as much N fertiliser than those of Janz. Uptake of N fertiliser by roots in the lower 0.7-1.0 m of the soil profile was similar in the vigorous lines and Janz. This indicates that the early and more extensive horizontal growth of the roots in the 0.2-0.7 m of the soil profile was responsible for the superior uptake of N by the vigorous lines. The implications of these genotypic differences in root growth and proliferation and their relationship with the early acquisition of N are discussed with emphasis on their role in improving the efficiency of N fertiliser uptake and reducing nitrate leaching, particularly in the sandy soils of the Mediterranean climatic region of Australia.