Bacteria are present throughout the GI tract but their pattern and concentr
ations vary greatly. Probiotics are living microorganisms that belong to th
e normal intestinal flora and are important to the health and well-being of
the host. The concept of probiotic therapy is still controversial; there a
re many data from in vitro and animal studies, however, to date the benefic
ial effects of probiotics in humans have mostly been demonstrated under poo
rly defined experimental conditions. Several experimental and clinical obse
rvations suggest a role for the intestinal microflora in inflammatory bowel
disease (IBD) pathogenesis and there is increasing evidence supporting the
potential therapeutic role for probiotics in the treatment of IBD. The use
of probiotics to treat GI infections has produced contrasting results; the
ir efficacy in the prevention or treatment of infective diarrhoea was evalu
ated in a large number of studies; however, the most convincing evidence of
their benefit concerns rotavirus infection in children. Future research ne
eds to focus on obtaining more precise information on the composition of th
e enteric microflora and the mechanisms of action of probiotics.