As a humanitarian civic action project, American and Peruvian military medical personnel established a temporary clinic in Dos Palos, Peru. Fecal specimens from 20 diarrheic children and 10 non-diarrheic controls were tested for common agents of diarrhea. Enteropathogens detected in diarrheic stools were enterotoxigenic Escherichia coli (ETEC; 30%), Aeromonas (20%), enteropathogenic E. coli (15%), and Campylobacter (15%). Isolates from control specimens were Aeromonas (10%) and Campylobacter (10%). ETEC-associated diarrhea was more common in this study (30%) than in three similar populations studied in Lima (2-16%). The results suggest that the northern coastal area of Peru is a relatively high-risk area for diarrhea caused by ETEC.