The National Influenza Surveillance Scheme includes data on influenza-like illness from sentinel general practitioner practices, laboratory reports of influenza from National Notifiable Diseases Surveillance Scheme and absenteeism data from a national employer. In 2004, 2,116 cases of laboratory-confirmed influenza-like illness were reported, which was 41 per cent lower than the previous year. Peak activity was recorded in September, a month later than in 2003. Influenza A was again predominant while influenza B had an increased activity compared to the previous season. Four hundred and fifty-four isolates were antigenically analysed: 342 were A (H3N2 strain), 4 were A(H1N1 strain) strains and 108 were influenza B viruses. Further antigenic drift was seen in the A(H3N2) subtype with approximately one third of all isolates antigenically distinguishable from the A/Fujian/411/2002 reference strain. Vaccination coverage indicated that 79 per cent of Australians aged over 65 years received the 2004 influenza vaccine.