Analysis of the deduced amino acid sequences of the HA and NA proteins indicated that the viruses had characteristics of highly pathogenic avian infl uenza. The HA cleavage site consists of multiple basic amino acids RE-RRRKKR (in 1 isolate, CU-329, REKRRKKR). All infl uenza subtype viruses harbor Glu-222 and Gly-224 at the receptor binding site, indicating preferential binding to the avian receptor SA-α-2, 3-Gal. In addition, the virus sequences contain 7 glycosylation sites as previously identifi ed in most isolates from Thailand (6) . A glycosylation site adjacent to receptor binding sites may help increase virus infectivity in host cells (7) . In some isolates, polymorphisms of amino acids related to antigenic properties of the viruses at position V86A, L138Q, and K140N were observed. All 12 subtype H5N1 viruses had a 20-aa deletion in the NA protein, typical for the NA stalk region of recent subtype H5N1 isolates (2003) (2004) (2005) (2006) (2007) (8, 9) . None of the subtype H5N1 isolates had any amino acids indicating oseltamivir resistance at the crucial positions 119 (E), 275