Field experiments in 1979 revealed that higher populations of Metopolphium dirhodum (Wlk.) developed on barley yellow dwarf virus (BYDV)-infected winter wheat and oats than on healthy plants. More Sitobion avenae (L.) were similarly recorded in 1980 on BYDV-infected winter wheat, oats and barley. In both years, foci of BYDV infection attracted more immigrant alates than did healthy plants. This observation was supported by laboratory flight chamber trials in which aphids were simultaneously presented with a choice of targets; both M. dirhodum and S. avenae alighted more frequently on the leaves of BYDV-infected oats and barley than on those of healthy plants. The adult size and fecundity of S. avenae were increased by feeding on BYDV-infected wheat, oats and barley but M. dirhodum was not affected. Both BYDV infection and aphid honeydew predisposed wheat ears to infection by Cladosporium. Individual M. dirhodum and S. avenae excreted less honeydew on BYDVinfected than on healthy wheat in the laboratory. The significance of the interactions between BYDV, its aphid vectors and C1adosporium is discussed in the light of the foregoing findings.