Bacterial translocation from the gastrointestinal tract and macrophage activation are central to current theories of sepsis. The relevance of both in obstructive jaundice is unclear. The effect of bile duct ligation for 7 days on bacterial translocation to mesenteric lymph nodes and on macrophage activation in a rat model was examined. Compared with an incidence of zero in sham-ligated controls, bile-duct ligated rats had a 67 per cent incidence of Gram-negative colonization of mesenteric lymph nodes. This was associated with a significant (P < 0.001) decrease in macrophage tumour necrosis factor, superoxide anion and nitric oxide production compared with that in sham controls. Spontaneous bacterial translocation occurs in experimental obstructive jaundice and is associated with marked suppression of macrophage activation. This suggests a mechanism whereby jaundiced patients may be more susceptible to persistent infection but relatively protected against uncontrolled sepsis.