Wheat is one of the most important food crops in the world and a staple diet of more than half of the world’s population (Johnson et al. 1978). The Russian wheat aphid (RWA) Diuraphis noxia (Mordvilko) (Homoptera : Aphididae) is a devastating insect pest of wheat and barley, causing severe yield losses and control costs valued at several hundred million dollars each year (Webster et al. 2000). Due to its habit of seeking refuge in infested rolled leaves, RWA is difficult to manage with insecticides or biocontrol agents. Hence, using resistant cultivars is an ecologically, economically and biologically sound way of managing RWA (Wiseman and Webster 1999). Several sources of RWA resistance have been identified and the genes from these sources have been used to develop cultivars. The identification of a new biotype of RWA - biotype ‘B’ - virulent to all known RWA resistance genes except Dn7 (Haley et al. 2004), has necessitated the identification and characterization of new sources of RWA resistance to both biotypes A and B. Wheat CItr (Cereal Introduction triticum) 2401 is resistant to both the RWA biotypes. An F_2:3 mapping population derived from crossing CItr 2401 with the susceptible cultivar (Karl) was used to determine the location of the Dn genes present in CItr 2401 controlling resistance to RWA biotype B. The results from the mapping experiments will be presented and discussed.