The translocation of indigenous bacteria from the gastrointestinal tract to the mesenteric lymph nodes was compared in 10 strains of mice. Indigenous Escherichia coli were cultured from the mesenteric lymph nodes of only 2 of the 6 mouse strains examined. Thus, spontaneous translocation of indigenous enteric bacteria across the intestinal barrier did not occur to any significant extent in any of the mouse strains examined. Since bacterial overgrowth in the gastrointestinal tract promotes bacterial translocation, bacterial translocation was tested in 10 mouse strains including B10 series after antibiotic-decontaminated and subsequent colonization with streptomycin-resistant E. coli C25. E. coli C25 populated the ceca of the mice at levels of 108-100/g and translocated to 90-100% of the mesenteric lymph nodes with mean of 101.13-101.86/mesenteric lymph node. There were no significant differences between mouse strains as to the translocation incidence or the numbers of viable E. coli C25/mesenteric lymph node. Thus, genetic differences between mouse strains did not influence bacterial translocation from the gastrointestinal tract to the mesenteric lymph nodes.