The use of phosphate as the limiting nutrient for scleroglucan formation by Sclerotium glucanicum led to stimulation of glucan formation. Final exopolysaccharide concentrations achieved in phosphate-limited (18.9 kg m-3) cultures were much higher than in the usual nitrogen-limited fermentations (11.4 kg m-3). The mechanism by which phosphate limitation engendered glucan formation may be largely non-specific, involving a generalised diversion of the carbon source away from biomass formation and towards glucan synthesis. The effect of stirrer speed was examined in a fermenter fitted with a 6-bladed Rushton turbine impeller of 0-5 vessel diameter. It was noted that biomass and scleroglucan formation showed different optima. This may have been due to the markedly different oxygen requirements of the two processes.