There are 91 species and varieties reported, including Physopella mexicana on Tripsacum lanceolatum in Durango, Puccinia chihuahuana on Muhlenbergia fragilis in Chihuahua, P. hilariae on Hilaria hintonii in Morelos, P. sierrensis on Muhlenbergia speciosa in Durango and Sinaloa, P. chisosensis Cummin. var. longa on Piptochaetium fimbriatum in Coahuila, P. vilfae Arth. & Holw. var. mexicana on Sporobolus buckleyi in Nuevo Leon and Tamaulipas, and Uromyces epicampis Diet. & Holw. var. durangensis on Muhlenbergia glauca in Durango. The only complete recording of the rust fungi of Mexico has been that of Arthur (1907-1927). Zenteno (1958) recorded 16 species of grass rusts and listed their hosts, localities, and collectors. Mexican material of grass rust fungi were considered, but not always listed, by Cummins (1953), Hennen and Cummins (1956), Greene and Cummins (1958), Cummins and Greene (1961, 1966), Ramachar and Cummins (1963, 1965), Hennen (1965), and Cummins and Husain (1966) in their monographic studies of rust fungi of various tribes and genera of the grasses. When the North American Flora (Arthur, 1907-1927) was published, the grass rust fungi were based almost solely on the collections of E. W. D. Holway, Edward Palmer, C. G. Pringle, and A. S. Hitchcock. These men collected around 1900. Holway was the only one specifically interested in fungi. He made 95 collections of grass rusts, mostly in the southern half of Mexico. His collections comprised about half of the total available when the Flora was written. In the early years of the operations of the Rockefeller Foundation, J. S. Niederhauser collected several grass rust fungi. More recent collections are those recorded by Zenteno (1958) and made mostly by Mexican botanists. I have seen some of these collections, especially those of E. Hernindez X., J. Rodriguez V., and C. Tapia J. In 1961, 1962, and 1963, I collected 260 specimens of rusted grasses, visiting all of the states north of, and including, San Luis Potosi and Zacatecas. The northern states were selected because of the dirth of information about 1 Journal Paper No. 2804 of the Purdue University Agricultural Experiment Station.