The objectives of this study were to determine the survival of avian influenza virus (AIV) subtype H5N1 under various physical and chemical treatments, including disinfectants, temperature and pH. The highly pathogenic AIVs subtype H5N1 were isolated from internal organs of suspected chickens and were characterized by the inoculation into chicken embryonated eggs (CEEs), hemagglutination (HA) test, hemagglutination inhibition (HI) test, reverse transcriptase polymerase chain reaction (RT-PCR) and nucleotide sequencing of hemagglutinin (H) and neuraminidase (N) genes. Three H5N1 isolates, at the concentration of 10(9) 50% embryo lethal dose (ELD(50))/ml, were used for the determination of the survival of the virus under different chemical and physical treatments. The chemical treatments were performed by incubating the viruses with various types of disinfectants including glutaraldehyde (Glu), hydrogen peroxide, quaternary ammonium compounds (QAC), Glu+QAC, iodine, chlorine, formalin and phenol, at 25 and 37 degrees C, for 0, 5, 7, and 14 days. The physical treatments included incubation of the viruses at 55, 60, 65, 70 and 75 degrees C for 10, 15, 30, 45 and 60 min or pH 3, 5, 7, 9 and 12. The results revealed that AIV H5N1 reference viruses, 2004.1, CUK-2/04 and 2004.2, showed low or no resistance against Glu+QAC, chlorine and phenol at both tested temperatures. Incubations at 70 degrees C for 60 min or at least 75 degrees C for at least 45 min could effectively inactivate all of the isolates, whereas all ranges of pH could not inactivate any of them. In this study, CUK-2/04 was more resistant to the disinfectants, temperatures, and pH compared to the other isolates.