Local and systemic reactions and antibody responses to three different doses of influenza virus vaccine (A/New Jersey/76 [Hsw1N1]) produced by four different manufacturers were studied. Local and systemic reactions that peaked between 8 and 24 hr after vaccine administration were related to the source of the vaccine more than to the dose. Antibody conversion occurred in almost 90% of subjects over the age of 25 years but in only 61%of subjects 25 years or younger. This low response rate was due almost entirely to the lack of response of volunteers who received split-product vaccine (only 49% of subjects became seropositive). In addition, individuals with symptoms of local reaction had a rate of antibody conversion and a magnitude of antibody response that were significantly higher than those observed in subjects who did not have local reactions. These findings suggest that in subjects older than 25 years, all four vaccines produced a high frequency of antibody response with a minimum of side effects. In addition, split-virus vaccine is less immunogenic than whole-virus vaccine in subjects younger than 25 years. Production of a vaccine devoid of local reaction may not be advisable.