The efficacy of a live Francisella tularensis vaccine strain to cause nonspecific immunity toward experimental legionellosis and listeriosis was studied. Immunisation with tularemia vaccine protected over 80% and 17% of experimental animals against subsequent lethal challenge with Legionella pneumophila and Listeria monocytogenes, respectively. The protection was maximal during the first month following immunisation and declined thereafter. In order to delineate the immunostimulatory moieties of the Francisella microbe, several cell wall proteins have been purified and characterized. However, isolated cell wall components failed to induce protection.