Five lots of a new highly purified (filter-purified) killed influenza virus vaccine were tested in varying regimens in adjuvant 65 or in aqueous formulation in a total of 708 persons in an institution. Adjuvant 65-type formulation containing 300 or 600 chick-cell agglutination (CCA) units of pentavalent influenza virus vaccine caused roughly fourfold more antibody to develop than did the corresponding aqueous vaccines. A single dose of 300 CCA unit adjuvant vaccine was about as effective in stimulating antibody as 600 CCA unit adjuvant vaccine and was greatly superior to two doses of 600 CCA unit aqueous vaccine. The antibody stimulated by the adjuvant was retained well for at least four months, at which time the responses to aqueous vaccine had usually declined substantially. Neither aqueous nor adjuvant vaccines caused significant local or systemic clinical reaction.