Abstract A description is provided for Pyrenochaeta oryzae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Oryza sativa . DISEASE: Sheath blotch of rice or known in Japanese as 'Yosho-kappanbyo' meaning sheath brown spot (Hashioka, 1972). The macroscopic symptoms are large brown lesions on leaf sheaths. At first lesions start from the margin of a sheath as dark brown oblong blotches which enlarge, become bluish-grey, finally covering the entire sheath. Lesions may reach up to 10 cm in length and often appear at the junction of sheath and leaf blade just below the collar without causing the collar to break. When dry the affected part of the sheath turns greyish-brown with or without distinct brown margins. GEOGRAPHICAL DISTRIBUTION: Africa (Sierra Leone, Swaziland); Asia (Burma, China, India, Japan, Malaysia, Philippines, Sri Lanka, Thailand); Australasia & Oceania (Fiji, Solomon Islands). TRANSMISSION: Presumably dispersed in the crop by splash-liberated conidia from infected leaf sheaths and glumes during wet weather. Lesions on leaves also appear at the site of oviposition of the green hopper, Nephotettix bipunctatus [Nephotettix virescens] (Hashioka, 1972).