We studied the interactions between nitrogen (N) inflow (uptake rate per unit root length) and root growth in the capture of nitrate by soil-grown wheat (Triticum aestivum L. cv. Wembley). [l5N]-nitrate was applied locally to soil overlying seminal roots of 42-d-old plants that had previously received K fertilizer (N +) or not (NO), [35S]-sulphate was also applied to check the specificity of the plant's responses to nitrate. NO plants had exhausted soil nitrate by day 42. Over the next 7 d, inflow was stimulated in soil to which [15N]-nitrate was supplied in the NO plants. NO plants increased their root length densities throughout the root system, not only around the point of [15N]-nitrate application. Root length density did not change in the N+ plants. NO plants captured 73 % of the [l5NJ-nitrate in 7d; N+ plants captured only 13%. There was no evidence that the plants' responses to the localized application of nitrate had an effect on the uptake of sulphate. The dominant influence on the capture of nitrate was inflow, rather than root growth.