The effectiveness of some vaccine preparations for the revaccination of hamadryas baboons after their primary immunization with live plague vaccine " NIIS " administered in the form of aerosol was studied. The study was carried out under the conditions of the aerosol challenge of the animals with Y. pestis. The subcutaneous injection of plague vaccine " NIIS " was found to have advantages over its aerosol administration. Revaccination with Y. pestis fraction I, absorbed, was found to be 8 times more effective than the administration of plague vaccine " NIIS " by inhalation and not inferior to the subcutaneous injection of this vaccine. Y. pestis lipopolysaccharide, when injected simultaneously with fraction I, produced an immunosuppressive effect. The development of chemical plague vaccine on the basis of fraction I, intended for revaccination, was shown to have good prospects.