Evidence for the role of probiotics in maintenance of health or prevention of disease is mounting and is supported in some cases by blinded, placebo-controlled human trials. Today, in an era of antibiotic-resistant pathogens and other looming microbial threats, the value of prevention of infection is recognized. Probiotics may play an important role in helping the body protect itself from infection, especially along the colonized mucosal surfaces of the gastrointestinal tract. Probiotic products are available in many different forms worldwide, including pills, powders, foods, and infant formula. In some cases, general health claims are made that cannot be substantiated for the specific strains and levels being used and consumers must therefore beware.