Travelers' diarrhea was studied prospectively in a group of 39 American Peace Corps Volunteers (PCVs) during their first five weeks in Kenya. Twenty-seven developed diarrheal disease and 12 remained well. Multiple episodes were documented in 11 of the symptomatic volunteers. Enterotoxigenic Escherichia coli of many serotypes producing heat-labile and/or heat-stable enterotoxin were isolated from 17 of the 27 volunteers with diarrhea and from 1 of the 12 well volunteers. The enterotoxigenic E. coli were more likely to be antibiotic sensitive than the non-enterotoxigenic E. coli. A serum antibody rise to the heat-labile toxin (LT) was detected in six symptomatic volunteers, five of whom had a positive culture for LT-producing E. coli, and from one asymptomatic, culture negative volunteer. Salmonella cubana was isolated from two volunteers, and three volunteers had serologic evidence of infection with human reovirus-like (rotavirus) agent. This study confirms the role of enterotoxigenic E. coli as a major cause of travelers' diarrhea and suggests that the disease is similar in widely separated geographic areas.