Intradermal immunization with recombinant L. monocytogenes vaccines protects mice against aerosol challenge with F. tularensis Type A SchuS4 strain. Ten groups of eight BALB/c mice were sham-immunized, or immunized i.d. twice at weeks 0 and 4 with 1×107 CFU rLmΔactA, rLm/iglC or rLm/katG. Mice immunized twice with 1 × 104 CFU LVS served as a positive control. Six weeks after the second immunization (week 10), mice were challenged by aerosol with F. tularensis SchuS4 with a dose estimated to be either 1 × LD100 (A) or 10 × LD100 (B). [(The effective dose actually delivered in (A) was less than 1 × LD100 as 50% of the animals survived, i.e. the dose was effectively 1 × LD50. The animals in (B) received 10 times the dose of the animals in (A), as detailed in Methods]. The difference in survival between the mice in a vaccinated group and mice in a sham- or vector-vaccinated group was evaluated using a logrank analysis. ns, not significant (P > 0.05).