Probiotics are live microbial organisms that are administrated as supplements or in foods to benefit the host. It is the recommendation that they may be helpful in the prevention and treatment of acute diarrhea in adults and children, the prevention of antibiotic-associated diarrhea in adults and children, and the maintenance of remission and prevention of pouchitis. Although early results indicate that probiotics may also be useful in immunologic modulation to prevent atopy, treatment of radiation intestinal disease, vaginosis, ulcerative colitis, and the irritable bowel syndrome, the studies available are not sufficient to say they are definitely helpful. Even fewer data are available to recommend probiotics for the treatment of H pylori and Crohn disease and for the prevention of cardiovascular risk factors or other degenerative diseases. Clearly, larger and better-designed studies of probiotics are necessary, including comparative and dose-ranging trials.