Diarrheal diseases remain a leading cause of morbidity and mortality in the developing countries and represent at least a nuisance in the industrialized world. Fluid and electrolyte replacement, particularly via oral rehydration, is the mainstay of therapy for the prevention and treatment of dehydration associated with these illnesses. Antibiotics are not indicated for the majority of enteric infections, and their promiscuous use can contribute to the escalating prevalence of bacterial resistance worldwide. Used judiciously, however, antimicrobial agents can ameliorate illness or curtail pathogen excretion and spread of disease, or both, in some diarrheal infections. Antimicrobial agents are indicated for shigellosis, cholera, traveler's diarrhea, amebiasis, and giardiasis. They are indicated in some specific circumstances to treat infections caused by Campylobacter, some categories of diarrheagenic E. coli, C. difficile, nontyphoidal Salmonella, and certain Vibrionaceae. Few adjunctive treatments provide proven benefit without risk of adverse reactions; most offer no advantage over placebo, and their general use is not encouraged.