Between 72 and 120 wheat [Triticum sp.] lines were tested annually 1970-1977, to characterize the reactions of various specific resistances to stem rust caused by 100-300 cultures of P. graminis f. sp. tritici that represented the ranges of pathogen virulence detected in the annual race survey. Annually, 10-100 cultures also were retested. The wheat genotypes that were studied can be classified in 3 groups based on responses to North American rust fungus cultures: those susceptible to all or nearly all of the cultures studied, i.e., Sr9f, 9g, 16, 18, 19, 20, 28, LC, McN and Kt''2''; those differential in response, i.e., Sr5, 6, 7a, 7b, 8, 9a, 9b, 9d, 9e, 10, 11, 12, 14, 15, 17, 21, 23, Tt-l, Tt-3, Tmp, dp-2, and X; and those universally resistant or nearly so, i.e., Sr13, 22, 24, 25, 26, 27, 29, 30, Tt-2 and Gt. Although the low infection types produced by a range of avirulent cultures on a host with the corresponding gene for resistance over a range of environmental conditions generally were similar, numerous exceptions were observed.