The objectives of this Cumitech are threefold. First, it will update information on the causes of bacterial diarrhea and techniques for their detection presented in Cumitech 12. Second, it will describe new agents of bacterial diarrhea and the means to isolate and identify them. Detailed procedures for identification of each species are found in the Manual of Clinical Microbiology. Third, it will outline cost-effective strategies for obtaining the highest possible yield from stool examinations. Particular emphasis will be placed on recognizing appropriate clinical situations in which various agents should be sought.