This placebo-controlled evaluation in elderly persons of inactivated influenza virus vaccines containing 200 or 400 chicke cell-agglutinating units of both A/New Jersey/76 and A/Victoria/75 antigens revealed mild systemic reactions in 7.8% and moderate reactions in 4.9% of vaccinees. These reactions were more common after administration of whole-virus than subvirion vaccines, more frequent in females than males, and more frequent in persons with low initial titers of antibody to A/New Jersey antigen. Local inflammation occurred in 18.7% of vaccinees (predominantly females) and frequently was seen with systemic reactions, but did not correlate with antibody response. Titers of antibody to A/New Jersey antigen were initially high and 99% of vaccinees had titers of greater than 1:20 after vaccination. Titers of antibody to A/Victoria antigen were initially low, and 56% of vaccinees had titers of greater than 1:20 after vaccination. Fourfold or greater increases in titer occurred in about 50% of vaccinees for each virus, most often concomitantly. Antibody responses to subvirion and whole-virus vaccines were similar, and increased responses with higher doses coincided with increased reactogenicity. Later revaccinations because of low titers of A/Victoria antibody produced negligible antibody responses.