We conducted a prospective study 77 indigenous African adults with acute diarrhea seeking care at the major hospital in Nairobi, Kenya, to determine the major pathogens responsible for this syndrome in adults. Fecal and blood specimens were collected and examined for enteric bacterial pathogens, viruses, and parasites. In 13 (26%) inpatients and 11 (49%) outpatients Shigella was found, and heat-labile and heat-stable forms of enterotoxigenic Escherichia coli were found in 9 (18%) inpatients and 1 (4%) outpatient. Human revirus-like agent titers rose significantly in another 3 (6%). Amebic dysentery was not seen although hemagglutination-inhibition tests for invasive Entamoeba histolytica were positive in 4 inpatients. An etiologic agent was found in 65% of patients.