Kohlrabi (Brassica oleraceavar.gongylodes) plants were grown in the greenhouse under autumn conditions and fertilized either with pellets containing nitrogen as 40% ammonium sulphate and 60% urea or with nutrient solution containing nitrogen predominantly as nitrate. Plants given nitrogen as ammonium ions developed glaucous leaves compared to those supplied with nitrate which formed glossy leaves. Ammonium-induced glaucousness was the result of a two-fold increase in the amount of epicuticular wax and a markedly altered fine structure. Leaves from ammonium fertilized kohlrabi plants also showed a 21% increase in chlorophyll content together with a reduction in the chlorophyll a:b ratio and decreased ground state fluorescence compared to plants supplied with nitrate. Photosynthesis and stomatal transpiration were unaffected by the form of supplied nitrogen.