Enterotoxigenic Escherichia coli, Vibrio cholerae O1, Campylobacter jejuni, Salmonella species, and Shigella species are major causes of morbidity and death in diarrheal disease. More recently recognized pathogens are V. cholerae O139 and enterohemorrhagic E. coli. In addition to this, several presumptive virulence factors have been identified in diarrheagenic E. coli and in other species. To confirm these as virulence factors we need good diagnostic tools and good epidemiological studies. These are of vital importance to create vaccines for diarrheal diseases.