The leaves of wheat infected by powdery mildew Erisiphe graminis var. tritici manifested repellent action against cereal aphids Rhopalosiphum padi and Sitobion avenae. Food (leaves) for aphids enriched in chemical components present in diseased leaves caused weaker reproduction of S. avenae and mortal i ty of R. pad i. It could be caused by post-infection increase of the level of monophenols and flavanoids in the leaves of wheat infected by powdery mildew (E. graminis var. tritici). These compounds increasing IAA-oxidase activity in plants can have a harmful influence on the cereal aphids.