By using two reporter protein-encoding virus-like RNAs derived from identical viral RNA (vRNA) segments, we assessed their incorporation efficiency into single progeny virions. Most plaques formed by the recombinant viruses that were generated in cells positive for both reporter genes expressed only one or the other protein. These results suggest that two virus-like RNAs encoding different reporter proteins compete for incorporation into virions, and individual influenza virions incorporate single, but not multiple, copies of homologous vRNA segments.