Inactivated influenza A/New Jersey/76 virus vaccines were administered intramuscularly to 199 normal adults, aged 19–59, in doses of 200, 400, or 800 chick cellagglutinating units in a double-blind, placebo-controlled trial. Systemic reactions (including fever) were uncommon, were mild, lasted <24 hr, and were more frequently associated with the largest dose. Local reactions were common but mild. A single, rapidly reversible, allergic reaction was noted in a volunteer 2 hr after vaccination. There was a trend toward fewer systemic reactions in vaccinees who had preexisting hemagglutination-inhibiting (HAl) antibodies to the vaccine virus in their sera as compared with seronegative vaccinees. All vaccine preparations at all three dosages evoked serum HAl titers of ⩾20 to ⩾40 in a high proportion of seronegative recipients, with significantly greater geometric mean titers at the highest dosage. Vaccinees between the ages of 19 and 23 years manifested significantly lower serologic responses than did vaccinees over the age of 23. Thus, normal adults over the age of 23 can be immunized with a single, well-tolerated dose of A/New Jersey /76 vaccines.