After growing barley (Hordeum vulgare L.) in nutrient solutions containing EDTA, uptake of the nutrient metals was determined at three harvests and concentrations of the various chemical species of each metal in the growth solutions was modelled by computer simulation. Complexation with EDTA had different effects on the uptake of the ions Fe3+, Mn2+, Cu2+, and Zn2+. At the highest EDTA level (EDTA/Fe=2/l) the plants were chlorotic and growth was inhibited. This is attributed to a deficiency in Zn rather than in Fe. The critical level of free Zn2+ required in nutrient solutions for healthy growth was found to be approximately 10−1010−10 mol dm−3, which is consistent with that found by earlier workers for other plant species. Barley tolerated much lower levels of the free ions of copper and iron without exhibiting any obvious adverse effects.