Eighty-four patients with serious infection due to Entamoeba histolytica were evaluated for systemic complications by objective criteria for dysfunction of the organ systems normally assessed in surgical sepsis. Of 71 patients with amebic liver abscess (ALA), 41% had systemic complications and 13% had more than one organ system involved. Patients =40 years of age and those being treated with steroids were at significantly increased risk of developing complications (P =.05). The erythrocyte sedimentation rate and the levels of the acute-phase markers C-reactive protein (CRP) and serum amyloid A (SAA) were significantly elevated in patients with ALA over values in those without ALA (P =.05). ALA patients with complications had lower CRP and SAA concentrations than those without complications (P =.05). Blood and liver aspirates in ALA patients were usually bacteriologically sterile. The pathogenesis of systemic complications and the associated acute-phase response requires further study, and ways of predicting disease severity and intervening therapeutically must be devised.