Live attenuated influenza virus (LAIV) vaccines present new possibilities for the prevention and control of influenza. Administered intranasally, LAIV vaccines offer a needle-free route of administration. These investigational vaccines have also been shown to be safe and effective in children and healthy working adults. A 2-year placebo-controlled trial among young children (1996-1997 and 1997-1998 influenza seasons) demonstrated that LAIV vaccine was associated with a 92% reduction in laboratory-confirmed cases of influenza. Vaccination also significantly reduced episodes of otitis media and antibiotic use. In a placebo-controlled trial among healthy working adults during the 1997-1998 season, LAIV vaccine significantly reduced episodes of febrile upper respiratory tract illness and illness-associated work loss, health-care use, and antibiotic use. Seventy percent of study participants self-administered the vaccine. An economic analysis of the benefits of LAIV vaccine in this population suggests that the break-even cost for LAIV vaccine and its administration for healthy working adults would be about $39. For both children and healthy adults, LAIV vaccine provided substantial protection during the 1997-1998 season when the predominant circulating virus, the A/Sydney variant, was not contained in the vaccine. Studies are still underway to evaluate the potential incremental benefits of LAIV vaccine in addition to inactivated vaccine in high-risk populations. LAIV vaccines will be an important addition to the armamentarium for fighting influenza.