A group of 23 volunteers were each inoculated with 600 CCA of a new form of influenza virus A/England/42/72 vaccine; this vaccine consisted of purified haemagglutinin and neuraminidase antigens adsorbed to alhydrogel. No significant reactions to the vaccine were reported. Twenty-two volunteers produced increased titres of serum HI antibody, and all showed increased titres of NI antibody after immunization. Thus, for volunteers with no pre-immunization serum HI antibody, the geometric mean titre of serum antibody increased from 1/5 to 1/196 after immunization. Ten volunteers developed local neutralizing antibody after immunization; this antibody response was detected most frequently in volunteers who showed the greater serum antibody response to immunization, and in nasal washings with the higher concentrations of protein and IgA. Ten weeks after immunization, the vaccinees and a group of matched controls were inoculated intranasally with attenuated A/England/42/72 virus. Evidence of infection with the challenge virus was found in 14 of the control subjects and in one of the vaccinees. The results indicate that the surface-antigen-adsorbed vaccine induced high titres of serum antibody, and gave significant protection against challenge infection.