Abstract: The invention concerns a fermentation process for the production of (+)-2-(5.beta.-n-butyl-4.beta.-hydroxy-2-oxo-tetrahydrofuran-3.beta.-yl)-2 .alpha.-methylacetic acid, which compound has useful ulcer-healing properties. The process is characterised by cultivating an organism known to produce dihydrocanadensolide, such as Penicillium canadense, under generally conventional conditions and then extracting the culture filtrate at a pH in the range pH 3.0-7.0 with a suitable solvent, such as ethyl acetate, and then evaporating the extract to dryness. In a preferred embodiment the extraction is carried out on the culture filtrate at pH 4.0-4.5.