WAR-TIME developments in high-frequency dielectric heating seemed to offer new possibilities in the control of seed-borne plant disease. By this method the temperature of the whole of a mass of grain can be raised fairly uniformly. It should therefore be superior to earlier means of dry heating, where, owing to the low thermal conductivity of the sample, the centre of the mass does not attain the required temperature when the outside is correctly heated. Hot-water treatment can maintain the necessary temperature throughout the mass, but is a slow and costly process in commercial practice. A method of uniform dry heating would find its greatest application in the control of internal seed-borne fungal diseases such as loose smut of barley and wheat. Experimental work with such diseases, however, necessitates the development of new techniques for evaluating the effect of treatment. Preliminary work was therefore carried out with the seed-borne phase of leaf stripe of oats (Helminthosporium avenæ). The amount of this disease can be estimated fairly rapidly by growing the oats to the seedling stage, or by plating out the seeds in petri dishes.