C3H/HeN mice (Nramp1+) were inoculated i.p. with a 1:1 ratio of wild-type and mutant S. Typhimurium strains: hmp (circles), hcp (squares), STM1808 (triangles), yeaR (inverted triangles), ygbA (diamonds), ytfE (open circles) and phoP (open squares). Competitive index (C.I.) for survival in mice was determined five days post-infection (Experimental Procedures) in livers (A) and spleens (B). Medians are indicated by horizontal bars. P-values were calculated using the Wilcoxon Rank Sum Test, n.s. denotes not significant.