Ring-width measurements on trees felled in a nitrogen-deficient pole-stage crop of Corsican pine on the sand dunes of Culbin forest (Morayshire) showed that, in addition to a growth check ascribed to the low nitrogen content of the soil, there was evidence for decreasing site quality, tree growth declining progressively with time. This feature is ascribed to the continuing immobilization of the limited nitrogen capital in the newly developing mor humus layer. Ammonium sulphate, at rates equivalent to 84, 168, 336, and 504 kg elemental nitrogen ha −1 , was applied to this crop when it was 36 years old, and the treatments repeated for a further 2 years. Nitrogen levels in the foliage rose from 0.9 per cent to as high as 20 per cent in the first year, increasing to 2.6 per cent after the third year of application. Response in terms of basal area appeared in the year after first application but was not accompanied by any changes in the pattern of growth throughout the season, nor was there a significant effect of tree size on the proportional change in relative basal area growth induced by the fertilizer, except for a slightly reduced response by the smallest trees to the lower rates of application. A similar low response by the smallest trees was found for height, but, in addition, height growth after treatment was greatest for the middle-sized trees, despite the fact that these had been growing significantly more slowly than the largest trees prior to application of the fertilizer. Form factor remained unaltered by the treatments but taper changed slightly. Height and basal area showed very different response patterns to the treatments. Thus, whereas maximum height growth occurred at the 168 kg N ha −1 treatment rate (2.41 m over 7 years, 1.4 times the control growth) maximum basal area growth occurred at the 504 kg N ha −1 rate, the highest rate used (13.0 m 2 ha −1 over seven years, 2.4 times the control growth); volume growth was maximum at the 336 kg N ha −1 rate (126 m 3 ha −1 over 7 years, 2.6 times the control growth). When related to levels of foliar nitrogen in the previous year, annual height growth was maximum at 1.6 per cent with maximum basal area growth occurring nearer 2.2 per cent. It is estimated that volume growth would be maximised at just over 20 per cent nitrogen.