The results of the study of the reactogenicity, safety and immunological activity of Russian cultural vaccine against hepatitis A are presented. The vaccine was found to have specific safety, moderate reactogenicity and pronounced immunological activity. In addition, the study of the prophylactic efficiency of the vaccine in the pre-epidemic period of the outbreak of hepatitis A morbidity in a group exceeding 14,000 adults was carried out. The study revealed high prophylactic efficiency of the vaccine (its efficiency rate was equal to 97.7%). On the basis of materials thus obtained vaccine "Hep-A-in-Vac" was recommended for use in medical practice for the prophylaxis of hepatitis A among adults.