An important concern relates to the transplanted stools themselves. Majdi Osman is clinical programme director at OpenBiome, the largest stool bank in the USA. “We exclude 97% of volunteers”, he told The Lancet Gastroenterology & Hepatology. [...] The vast majority of exclusions occur at the clinical interview. “Only physicians can collect the material, and we vet all the centres who apply to make sure that they have the facilities to administer it safely”, adds Osman.