The establishment of reverse genetics methods to manipulate influenza virus genomes has allowed the generation of recombinant (transfectant) influenza viruses expressing foreign sequences. Strategies for the construction of influenza virus vectors include the insertion of foreign epitopes into influenza virus glycoproteins, the expression of polyproteins, and the rescue of bicistronic genes into infectious viruses. Influenza virus vectors have been obtained which express both B- and T-cell epitopes from different pathogens. These constructs have been shown to mount in immunized animals systemic and local antibody responses, and/or cytotoxic T-cell responses against the expressed epitope. The available evidence suggests that influenza virus vectors may be attractive candidates for the development of effective vaccines against different diseases.