The Russian wheat aphid (RWA) Diuraphis noxia (Mordvilko) (Homoptera : Aphididae) is one of the most devastating insect pests of wheat and barley in the world. Yield losses and control costs are valued at several hundred million dollars each year (Webster et al. 2000). Due to their habit of seeking refuge in rolled plant leaves, it has been difficult to manage RWA with insecticides or biocontrol agents. Hence, the use of RWA resistant cultivars is an ecologically, economically and biologically sound way of managing RWA (Wiseman and Webster 1999). The effects of 11 cereal RWA resistance genes (Dn genes) have been categorized as reduced RWA growth rate (antibiosis to RWA) and increased compensatory plant growth (tolerance to RWA damage) (Hawley et al. 2003, Hein 1992, Smith et al. 1991). Several Dn genes have been used to develop cultivars resistant to RWA. Haley et al. (2004) reported the identification of a new RWA biotype, biotype ‘B’ which is virulent to all known Dn genes (as well as all current U.S. resistant cultivars) except the Dn7 gene. Hence there is an immediate need to identify and characterize other sources of RWA resistance to both biotypes A and B. In this paper, we report the categories of resistance expressed by a cereal introduction (CItr) 2401 that is resistant to RWA biotype B.