The protective role of virus-neutralizing antibody was demonstrated in Ebola virus-infected animals (Papio hamadryas) used in experiments on the development of passive humoral immunity by using specific immunoglobulin. Two immunizations of the monkeys with purified concentrated Ebola virus antigen with complete Freund adjuvant was shown to confirm intensive immunity to subsequent challenge protecting 80% of the immunized animals. It is concluded that effective preparations may be developed for specific prophylaxis of Ebola fever.