Factors contributing to the species richness of fungal pathogens infecting grasses were explored through statistical analyses of data derived from a computerized data base on fungi on plants in the United States and from grass floras. The total number of fungal species infecting each grass species, as well as numbers of smuts, rusts, and systemic clavicipitaceous fungi, were compiled. Host characteristics included grass subfamily, the number of species in the genus, geographic range, life history, and their status as native versus alien species, and crop versus noncrop species. Analyses indicated that the best predictor of pathogen species richness per host is host geographical range. Grass subfamily, life history, and status as crops or native species also were significantly correlated with pathogen load but explained less variation than host geographical range. Pathogen species richness per host showed a strong trend to increase with increasing latitude. Extensive sampling of fungal pathogens from selected grass species is needed to provide an independent measure of accuracy of the data base.Key words: biodiversity, fungi, grasses, pathogens, species richness.