Most wheat varieties growing in the vicinity of Hays, Kansas, are susceptible to races of Puccinia graminis f. sp. tritici that are common in central United States. However, they are seldom severely damaged by stem rust. It is commonly thought that weather in that area is not favorable for establishment and development of stem rust. In 1960 to 1965 the epidemiology of stem rust was studied at Hays in fields of Cheyenne wheat inoculated with urediospores of race 56 when the plants were in tillering to boot stages of growth. Infection occurred in all 6 years. Rust increase was related to the frequency of days when conditions were favorable for infection. Plots with initial intensities of 2.5 to 20 pustules per 100 culms were compared. In the 6 consecutive years 1960 to 1965 severities at soft dough stage were about 30, 25, 7, 2, 2, and 20 yields for rusted plots were 20, 19, 25, 34, 22, and 18 buacre and yields for adjacent control areas were 46, 29, 45, 35, 29, and 62 buacre, respectively. In 1965, a natural epidemic of stem rust caused severe damage to wheat in Kansas and Nebraska. In 1965, the crop ripened late in the season. In 5 of the 6 years, weather was favorable for rust epidemics. Late natural infection appeared to be the primary factor limiting severity of the rust epidemics.