In greenhouse pot experiments and field trials, leek cv. Albana plants were supplied with different amounts of N fertilizer at various growth stages. Leaf emergence, expansion, size and senescence were monitored. The rate of leaf appearance was not affected by N treatments and almost constant across experiments at 0.15/day. The rate of leaf expansion and the mature leaf area increased with leaf number, reaching maximum values between leaf numbers 11 and 14 and decreasing with higher leaf numbers. Both variables increased with increasing N application rate. The duration of leaf expansion was more or less constant across leaf numbers and not influenced by N treatments; the leaf expansion rate was the main factor determining mature leaf area. The rate of leaf senescence was not influenced by N treatments. Differences in total green leaf area per plant were caused by differences in the area of individual mature leaves and not by differences in the number of leaves. The specific leaf area of all leaves was more or less constant at 100 cmsuperscript 2/g.