Severe leaf blotching in a crop of barley growing on a red-brown earth (Calcic Rhodoxeralf) was closely associated with high concentrations of boron in the soil. No infection by fungal pathogens capable of accounting for the symptoms was found. Of 14 elements determined in the plants only accumulation of high-concentrations of boron was associated with the disorder. Boron concentrations in saturation extracts of subsoil ranged up to 17.9 µg boron/cm3 under plants that were severely affected, and plants sampled just prior to anthesis contained up to 96 fig boron/g (mean 62.4). Plants that were only slightly affected contained less than 15 µg boron/g (mean 13.8). Grain yield was depressed by 17% due to the boron toxicity. This is only the second report of boron toxicity due to naturally occurring boron in Australia, and the first for a red-brown earth.