Process temperature strongly influences the outcome of the fermentation process for production of the biopolymer scleroglucan using the mould Sclerotium glucanicum. Scleroglucan formation is optimal around 28 degrees C and falls as temperature is varied from this. Biomass formation displays a higher optimum temperature and a broader optimal range. Formation of the by-product oxalic acid generally rises as temperature declines, except at 20 degrees C, where oxalic acid formation accounts for only half of total acidity; the remainder is accounted for by malic and fumaric acid synthesis. At the highest temperature examined (36 degrees C), growth and biosynthetic activity were much reduced and the organism aggregated to form dense, heavily pigmented pelleted structures.