Recent reports have described the detection of cyanobacteria (blue-green algae)-like bodies (CLB) in the stools of persons with a prolonged syndrome of diarrhea, anorexia, and fatigue (1-3). In each of these reports, affected persons either were immunocompromised or had recently traveled to tropical countries. During 1989 and 1990, the first three reported outbreaks of this CLB-associated syndrome occurred in immunocompetent populations, affecting at least 150 persons. This report summarizes investigations of these outbreaks, which occurred in Chicago in 1990 and in Kathmandu, Nepal, in 1989 and 1990.