Scald is a disease of barley and some grasses caused by the fungus Rhynchos-porium secalis (Oud.) Davis. Lesions on naturally or artificially infected leaves begin as grey, water-soaked areas 8-12 days after inoculation. Frequently, lesions at this stage become dry but retain a grey-green colour which persists even when the un-infected parts of a leaf have become senescent and straw-coloured. More usually the lesions become oval-shaped with dry, pale-brown or white centres surrounded by dark-brown margins. We have also observed signs of hypersensitive reactions in artificially and naturally infected barley leaves. The hypersensitive reactions result in the formation of small dark-brown patches on the leaves where infection has been unsuccessful.