This report updates the 2003 recommendations by the Advisory Committee on Immunization Practices (ACIP) on the use of influenza vaccine and antiviral agents (CDC. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices [ACIP]. MMWR 2003;52[No. RR-8]:1-34). The 2004 recommendations include new or updated information regarding 1) influenza vaccine for children aged 6-23 months; 2) vaccination of health-care workers with live, attenuated influenza vaccine (LAIV); 3) personnel who may administer LAIV; 4) the 2004-05 trivalent inactivated vaccine virus strains: A/Fujian/411/2002 (H3N2)-like, A/New Caledonia/20/99 (H1N1)-like, and B/Shanghai/361/2002-like antigens (for the A/Fujian/411/2002 (H3N2)-like antigen, manufacturers may use the antigenically equivalent A/Wyoming/3/2003 [H3N2] virus, and for the B/Shanghai/361/2002-like antigen, manufacturers may use the antigenically equivalent B/Jilin/20/2003 virus or B/Jiangsu/10/2003 virus); and 5) the assessment of vaccine supply and timing of influenza vaccination. A link to this report and other information regarding influenza can be accessed at http://www.cdc.gov/flu.