Brusone causes considerable damage in Hungary in years with cool, sunless summers. The disease only occurs on certain soil types. The observation, which has been made several times, that healthy and diseased plants may be separated in paddy fields along a straight line, together with histological and biochemical examinations, indicate that the brusone is a soil-borne physiological disease. It has been established by ecological observations and chemical, microbiological, meteorological, histological and physiological investigations that the primary cause of the disease is H2S. This compound kills the roots of the rice plant. The occurrence of fungi (Piricularia, etc.) is merely a secondary phenomenon and is probably connected with disturbance of the nitrogen metabolism of the plant.