Objective To investigate HA1 hemagglutinin variant of influenza viruses isolated from children with influenza-like-illness (ILI) patients in Beijing in the 2004—2005 season and all viruses were subtype H3 at low titer of HA.Methods RNA of the 22 strains of influenza A type (H3) from the ILI children was extracted, HA1 fragment of hemagglutinin (HA) gene was amplified by RT-PCR and analyzed by bioinformatic softwares.Results 987 bps of HA1 coding 329 amino acid, which 22 strains influenza A type (H3 subtype)...