A clinical and serologic follow-up of 307 BALB/c mice and 12 rabbits injected with the blood and brain and spinal tissue of mice infected with 5 strains of T. pallidum has demonstrated the possibility of a prolonged (up to 465 days) preservation of pathogenic T. pallidum strains in these mice, as well as the regularity of a syphilitic infection development in rabbits. This permits recommending T. pallidum pathogenic strains to be maintained in mice at laboratories of institutions for skin and sexually transmitted diseases where experimental and diagnostic studies with the use of specific serologic tests for syphilis are carried out.