In severa l intestinal disease states, altered micro ora, impaired gut barrier and:or intestinal in ammation offer a rationale for the effective therapeut ic use of probiotic microorganisms. However , for most candidat e probiotic organisms there is a lack of evidence detailing their characterisation and effects on host ora and immunity. We have previously reported the isolation and characterisation, from surgically resected segment s of the huma n gastrointestinal tract (GIT), of potential probiotic lactic acid bacteria (LAB). We have also described subsequen t animal experimen ts that evaluated the establishment , persistence and localisation of speci c probiotic Lactobacillus strains within the murine intestinal tract, in addition to their ability to in uence the developmen t of murine in ammatory disorders. In these studies, transit and surviva l of Lactobacillus salivarius U CC118 at the ileum was demonstrat ed using enteral tube sampling of six healthy volunteer s following consumption of a single dose (150 ml) of fermented milk-born e probiotic (10 8 colony forming units per ml (CF U :ml)). Subsequently, we performed a randomised controlled trial of 80 volunteer s fed strain UCC118 (10 8 CF U:day for 21 d), using two oral delivery vehicles (fresh milk, n ¾ 20 vs. fermented milk, n ¾ 20; controls, n ¾ 20 for each). Throughout this feeding period , and for up to 100 days following cessation of feeding, the number s of total culturable lactobacilli and of the administered Lactobacillus U CC118 present in faeces were monitored. F ive subjects (5:40; fresh milk, four; fermented milk, one) were still excretin g the probiotic lactobacilli 21 days post-cessatio n of feeding, while one subject (fermented milk) was still colonised up to 100 days after feeding. Consumpt ion of fermented milk-born e UCC118 cells resulted in signi cantly increased levels of faecal-borne enterococci and lactobacilli. N umber s of bi dobacteria, coliforms and bacteroides were not signi cantly altered. In addition, changes in salivary IgA levels against U CC118 cells and increased granulocyt e phagocytic activity were observed following consumption of the fermented milk-borne probiotic. In summary, Lactobacillus UCC118 was found to effectively transit (and persist within) the human intestinal tract, to modify the faeca l ora and to engage the immune system.