There is great interest in the measurement of volatile organic compounds (VOCs) in breath and vapours from various human tissues (urine, stool, blood) in the diagnosis and monitoring of a wide range of diseases. VOCs emitted from stool are responsible for stool odour and consist of a large number of carbon based molecules of low molecular mass (<1.5Kd) including organic acids, alcohols, esters, heterocyclic compounds, aldehydes, ketones and alkanes. They result from the metabolism of the intestinal mucosa and the gut microbiota and their abundance changes according to the specific effects of intestinal diseases on these processes.