Technical Abstract: Race TTKSK (syn. Ug99) of Puccinia graminis f. sp. tritici, recognized for possessing virulence to the stem rust resistance gene Sr31, was first identified in Uganda in 1998. Since then, TTKSK has been identified in Kenya in 2005 and Yemen in 2006. In addition to virulence to Sr31, race TTKSK was found to be virulent to many resistant genes that are commonly used in breeding, and is considered as a major threat to wheat production in areas where stem rust occurs and a large number of current cultivars are susceptible. Two new races, TTKST with virulence to Sr24 and TTTSK with virulence to Sr36, were identified in Kenya in 2006 and 2007, respectively. The virulence profile of TTKST and TTTSK is similar to that of race TTKSK on most of the known stem rust resistance genes. Simple sequence repeat (SSR) markers were used to examine the genetic relationship between isolates of these races. All isolates of the "TTKS" group shared an identical SSR genotype. Virulence profile and SSR genotype suggest that the TTKS group is a distinct lineage and that races TTKST and TTTSK might be recent in origin. Because of their broad virulence to stem rust resistance genes in the adapted germplasm, these races present a major challenge for developing resistance in breeding.