Probiotic bacteria such as lactobacilli and bifidobacteria have in the past two decades been increasingly used and promoted in yoghurts, fermented milks, and other foods and pharmaceutical products for their anecdotal health benefits. By the mid-1990s however, it was apparent that there was a scarcity of rigorous scientific clinical studies and published evidence that these bacteria could positively influence the balance of the human intestinal microbiota or, importantly, the health of consumers. The PROBDEMO project (Demonstration of the Nutritional Functionality of Probiotic Foods, CT96-1028), a multi-centre European collaboration, was established to address this lack of knowledge. The research partnership linked multidisciplinary groups from across Europe, building on the strong Scandinavian experience in probiotics (Table 1). The ultimate aim of PROBDEMO was to demonstrate the influence of probiotics on the intestinal microbiota and human health using properly controlled human clinical pilot studies.