One of the nonspecific defense mechanisms of higher animals is their ability to limit iron availability to infecting bacteria. Thus it has been argued that all pathogenic bacteria must have special mechanisms to obtain iron in the host environment. Salmonella typhimurium is known to produce a siderophore, enterobactin, with which it can obtain iron from host transferrin. Previous studies have indicated that the production of this molecule is necessary for the ability of intraperitoneally injected S. typhimurium cells to cause mouse typhoid, a largely intracellular infection. We have reexamined this finding with wild-type S. typhimurium and isogenic strains carrying the nonenterobactin-producing mutation ent-1 or ent-7. Our findings demonstrate that, although enterobactin production is necessary for growth in normal mouse serum, it does not affect the ability of S. typhimurium to cause mouse typhoid. Based on these findings and published results of other investigators on the role of siderophores in intracellular pathogens, a more comprehensive investigation of the importance of siderophores in intracellular infections may be warranted.