All gene segments of influenza virus share a common feature at their respective termini. Both the 5'- and 3'-terminal sequences are highly conserved and possess partial inverted complementarity. This allows for the formation of a double-stranded duplex, which plays a major role in transcription, replication and packaging of the viral genome. In vitro studies have shown that the viral polymerase binds to short RNA molecules containing these termini. In this study, attempts were made to test whether mini-RNA decoys containing either or both termini can inhibit the activity of the viral polymerase in vivo. RNA molecules containing either the 5' or the 3' noncoding sequences were unable to inhibit NS-CAT RNA replication, while mini-RNA decoys consisting of both the 5' and 3' noncoding sequences of vRNA or cRNA were able to efficiently inhibit the activity of the viral polymerases expressed from vaccinia virus vectors.