Diffuse-adhering Escherichia coli (DAEC) as a putative cause of diarrhea in Mayan children in Mexico. Diarrhea is a major cause of infantile morbidity and mortality in developing countries. A community-based, case control study was conducted in a southern Mexican Mayan village for 3 weeks during the peak diarrhea period to prospectively identify the infectious agents associated with childhood diarrheal disease. Several enteropathogens were isolated from stools of 34 of 58 cases, although none was significantly associated with diarrhea. For the 24 cases from which no enteropathogens were isolated, diffuse-adhering Escherichia coli (DAEC) strains were significantly associated with diarrheal disease (P less than .02; odds ratio = 6; 95% confidence limit, 1.08-99.0). DAEC were highly heterogeneous with respect to plasmid content and serotype. Three DNA probes designed to differentiate E. coli exhibiting localized, diffuse, or aggregative adherence were compared with results from a standard HeLa cell binding assay to assess the utility of these probes in the field. This study provides evidence for the potential pathogenic capacity of DAEC and underscores the variety of diarrheal agents operating within a community. 