Each individual has a unique, relatively stable, intestinal microbiota which plays an important role in human health. One of the side effects of antibiotic intake is a disturbance of this microbiota which can result in antibiotic-associated diarrhoea (AAD). It was widely assumed that these disturbances were short-term but recently medium and long-term disturbances have been described. The exact clinical consequences of these microbiota disturbances are not yet clear but they are associated with a multitude of disorders such as IBS and allergy. Knowledge of the effect of antibiotics on the intestinal microbiota and ways of restoring their unique composition are therefore of clinical importance. A RTC performed by the Maastricht University Medical Centre showed that the probiotic Ecologic® AAD was not only able to reduce AAD but also to restore the intestinal microbiota towards the pre-antibiotic state.