Abstract A description is provided for Pythium graminicola . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Agropyron cristatum, Avena saliva, Bromus inermis, Hordeum vulgare, Oryza saliva, Panicum miliaceum, Phleum pratense, Saccharum officinarum, Secale cereale, Setaria glauca, Sorghum vulgare, Triticum aestivum, Zea mays . DISEASE: Seedling blight, collar and root rot of wheat, maize, sugar-cane, and other Gramineae . GEOGRAPHICAL DISTRIBUTION: Africa (Mauritius, South Africa, Sudan); Asia (Ceylon, India, Indonesia, Malaya, Philippines, Taiwan); Australasia & Oceania (Australia, Hawaii); Europe (England, France, Italy); North America (Canada, Mexico, U.S.A.); Central America & West Indies (British Honduras, Jamaica, Puerto Rico, Salvador); South America (Argentina). (CMI Map 296) TRANSMISSION: Soil-borne. Most prevalent at depth of 3-6 in. and infrequent at 27-30 in. (38: 396), surviving in soil as oospores whose germination is stimulated by contact with growing roots of gramineous plants. Host roots may thus be used as traps for isolating the pathogen from the soil (37: 649; 41: 583).