Subunit influenza vaccines have the advantage of purity and a broad dosage range. Clinical studies were done with a new subunit vaccine produced by detergent fractionation with tri-(n-butyl) phosphate (TNBP). Acceptability by the recipients was compared in volunteers given 400 CCA units of A2 and 300 of B Influenza vaccine as either Sharples, zonal centrifuged, ether subunit, or TNBP subunit bivalent vaccines. When given subcutaneously, subunit vaccine caused only slightly less pain and erythema induration than zonal or Sharples vaccine. Compared with the i.m. route, the same vaccine given subcutaneously produced twice the local pain and eight times the erythema induration. Fever was infrequent and low grade by either route. HI antibody rises were good in all groups. Increasing dosages of TNBP vaccine up to 6400 CCA units of A2 and 4800 of B given i.m. as monovalent vaccine, produced no local and few febrile responses. An augmentation of the antibody titre occurred with the highest CCA unit dosages. Subunit vaccine given i.m. permitted administration of high CCA unit dosage beyond that accepted for standard vaccine without any increase in local reactions and with a measurable increase in antibody production and the induction of antibodies against related heterologous strains.