Purpose: Fungal‐type dysbiosis (FTD) is still an unproven diagnosis. Patients are polysymptomatic, but most have symptoms of irritable bowel. Treatment, using a diet low in fermentable, yeasty and mould‐containing foods with or without antifungal drugs, is often rewarding. Patients with FTD show elevated blood ethanol levels after fasting glucose challenge. Because of this most authors suggest a fungal cause. Hydrogen generation is a bacterial fermentation product and would only be expected if a bacterial cause was present. It was therefore decided to correlate ethanol and hydrogen production.Design: Statistical comparison of ethanol producers and non‐producers with respect to breath hydrogen and symptomatology.Materials and Methods: The gut fermentation profile was performed by gas‐liquid chromatography, and measured ethanol, a number of higher alcohols and short‐chain fatty acids. Lactulose breath hydrogen estimations were by gas chromatography. Statistics were calculated using Pearson's rank correlation and the chi‐squared test, using Microsoft Excel packages.Results: Two groups were studied. The first produced excess ethanol (n=18) and the second (n=20) did not. Both groups included patients producing hydrogen. There was no statistical correlation between levels of ethanol and hydrogen production.Conclusions: If FTD is solely due to yeasts, our ethanol positive group should not produce hydrogen, solely a bacterial ferment, but the ethanol negative group should. If the conventional view, that yeasts do not produce hydrogen as a fermentation product, is correct, it appears from the commonness of breath hydrogen positives in this series that bacterial fermentation is in some way implicated in FTD.