Quantitative relationships were established which defined the partitioning of nitrogen and dry matter between the leaves, stems and roots during the development of field grown lucerne. The coefficients were unaffected by whether or not N fertilizer was applied. The average % N in the aerial tissue fell sharply with increase in plant mass when aerial DM of the crop exceeded 1 t ha" 1. This was mainly because the proportion of stems increased and the % N in stems was low. The often-reported decline in % N with decrease in light intensity and increasing depth within the canopy was largely onset by a. decline in specific leaf weight, so that the average % N of the leaves declined only slightly as the plants grew. The average % N of the entire plant (aerial plus root tissues) remained constant at about 2-4 irrespective of plant size. After cutting, regrowth was accompanied by a rapid transfer of up to 40 kgN ha" 1 from root to shoot, but this loss was made good by N fixation during the main growing period.