A new method for rapid screening of high-yielding reassortants of influenza virus, as candidates for vaccine production, is described. Oligonucleotide probes specific for all the parent genes of A/PR/8/34 (PR8), except the HA and the NA were designed based on database information available for different influenza strains. Digoxigenin labelled probes were tested by slot-blot hybridizations to purified RNA from a panel of A/PR/8/34 wild type and A/PR/8/34 reassortant viruses. The results show that the vast majority of reassortants selected for their high growth yield had acquired the non-structural (NS), matrix (M) and RNA polymerase 2 (PB2) genes from the PR8 parent. It is proposed that probes for these genes provide the potential for a simple and rapid procedure for selection of candidate high-yield reassortants for vaccine production.