To address whether the internal gene segments of a highly pathogenic H5N1 avian influenza virus, associated with a fatal human case, contribute to disease severity, we generated a recombinant influenza virus (6:2 Tky/05) with the six internal gene segments from influenza H5N1 A/turkey/Turkey/05/2005 virus (Tky/05) and the HA and NA genes from the laboratory adapted strain PR8. The gene discussed is XK; the disease is influenza.