Mutations in and near the Salmonella typhimurium histidine transport operon were generated by insertion of the translocatable tetracycline-resistance element Tn10. Deletion mutants affecting histidine transport genes were subsequently isolated in several of the Tn10-containing strains. Tn10 insertions in hisJ occurred preferentially at one site, designated site A. This same site was also the preferential endpoint of deletions originating from Tn10 insertions at two neighboring sites. Thus, Tn10 insertion and Tn10-stimulated deletion formation appear to involve a common DNA-recogition step.