The inherited resistance of inbred mouse strains to Salmonella typhimurium injected subcutaneously has been reported to be controlled primarily by a single gene designated Ity. Resistant mice have the dominant allele Ityr and sensitive mice are homozygous for the recessive allele Itys. This paper describes studies undertaken to locate the gene using readily distinguishable phenotypes as chromosome markers. Appropriate F1 backcross and F2 generations of hybrids between resistant and susceptible inbred strains of mice, with or without the particular phenotypic markers, were tested both for susceptibility to salmonella sci and presence of the marker. Independent segregation of the characteristics eliminated all chromosomes except Chromosome 1. C57L mice resistant to S. typhimurium, Ityr Ityr and leaden, ln ln, located on Chromosome 1, were crossed with BALB/c mice sensitive to S. typhimurium and non-leaden. In the F2 generation mice, ln always segregated with Ityr. The presence of only one leaden mouse sensitive to S. typhimurium out of sixty leaden F2 mice tested linked Ityr closely with ln on Chromosome 1. This result will be of use in further experiments with hybrid populations by enabling us to predetermine resistance or sensitivity to S. typhimurium without infecting the mice, so permitting experiments on the nature of the inheritance in unsensitized mice.