Bird cherry-oat aphid, Rhopalosiphum padi L., is a serious pest of barley, Hordeum vulgare L., world-wide.  It is the most efficient vector of barley yellow dwarf virus, the most important viral disease of small grains in the world.  Not all bird cherry-oat aphids acquire the virus while feeding on infected plants yet yield loss has been reported with nonviruliferous bird cherry-oat aphid feeding alone.  Because bird cherry-oat aphid injury is normally considered asymptomatic, screening of seedlings in the greenhouse to identify resistance has not been considered possible.  A greenhouse seedling screening technique is herein proposed to identify bird cherry-oat aphid resistance in barley and a visual chlorosis rating scale of 1-5 is described.  The objectives of this study were to validate this screening technique and determine if the proposed rating scale accurately predicts resistance in terms of grain yield and yield components.