The diseases ulcerative colitis (UC) and Crohn’s disease (CD), collectively called inflammatory bowel disease (IBD), are increasing in incidence. They represent a substantial burden of disease for the individual and for society, as they are chronic with a relapse pattern of high frequency. The causes of these diseases are not known, but in the aetiology of both, dysbiosis of the intestinal flora is seen as central, and is currently the focus of intense research. AIM: the aim of this paper is to assess whether interventions on the microbiome in the form of probiotics, prebiotics and faecal microbiota transplantation or a combination of these can shed light on the underlying causal mechanisms of the diseases. METHOD: a literature search was done in PubMed, which resulted in 55 articles, of which 40 were chosen for further scrutiny. RESULTS: manipulation of the microbiome has varying and uncertain effects on IBD, with more promising results shown on UC than on CD. One conclusion is that there is needed more quality studies to attain more evident data. There is especially insufficient research with interventions on CD, and a complete lack of studies of faecal microbiota transplantation on CD. Some studies give insights into mechanisms that look promising for further research.