In order to study the relationship between the presence of circulating immune complexes (CIC) and the severity and duration of acute dysentery, we studied 11 adults and 45 children in Bangladesh with bacillary and amebic dysentery, using the Raji cell and solid-phase C1q (C1q-SPA) assays. CIC were found in 70% of patients with shigellosis and in all eight cases of amebic dysentery. Mild shigellosis was associated with positive samples in the first week of clinical illness, whereas severe cases, including those with the hemolytic-uremic syndrome, had negative admission assays but positive convalescent assays. Samples positive in the first two weeks of illness were more likely positive by the Raji cell assay alone whereas samples in the third and fourth weeks of illness were positive more often by the C1q-SPA assay. Only one shigellosis sample was positive by both assays. In amebiasis 11 of 13 samples were positive by the Raji assay alone. In dysenteric disease circulating immune complexes probably represent the failure of the inflamed mucosa to exclude microbial and dietary antigens, and suggest that the presence of CIC in any intestinal disease must be interpreted with caution.