This report updates 1998 recommendations by the Advisory Committee on Immunization Practices (ACIP) on the use of influenza vaccine and antiviral agents (MMWR 1998;47[No. RR-6]:1-26). The principal changes include a) information on the influenza virus strains included in the 1999-2000 trivalent vaccine; b) discussion of the potential expanded use of influenza vaccine; c) new background information on live-attenuated influenza vaccines (LAIVs), neuraminidase-inhibitor drugs, and rapid diagnostic tests; d) new information on the epidemiology of influenza among travelers; and e) the addition of referenced citations. This report and other information on influenza can be accessed at the website for the Influenza Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC at .