Abstract: The construction of a mutant in the phoP gene by means of homologous recombination from a clinically isolated Mycobacterium tuberculosis reduces the virulence thereof in mouse bone marrow macrophage. Moreover, the phoP mutant reduces the virulence thereof in the experimental mouse model. Said phoP mutant can persist without being eliminated both in the macrophage and in the mouse. Mice inoculated with the phoP mutant are protected against M. tuberculosis infection. The use of mutants of mycobacteria in which the phoP gene or the genes regulated by phoP have been inactivated are candidates for vaccines against human and animal tuberculosis as well as possible recombinant vaccines against other pathogens.