AbstractHepatitis A virus (HAV) strain CR326, adapted to grow in LLC‐MK2 cells, was highly purified, inactivated with formalin, adsorbed to alum, and tested for capacity to induce antibody to HAV in both mice and marmosets. The minimum dose of HAV antigen necessary to produce antibody in 50% of mice was 10 ng. As little as three doses of 1 ng each produced antibody in 50% of marmosets. Further, all marmosets with any detectable antibody to HAV, as a result of vaccination, were protected against virulent infection on challenge with HAV. Thus a highly efficacious, inactivated hepatitis A vaccine can be produced from virus grown in cell culture. Although LLC‐MK2 cells are unacceptable for use in human vaccine preparation, HAV can also be prepared in a similar manner in MRC‐5 cells, which are acceptable for human vaccine manufacture.