Sclerotium glucanicum NRRL 3006 was cultivated in a 120 dm(3) working volume airlift reactor with external recirculation loop for the production of the exopolysaccharide (EPS), scleroglucan. When culture pH was not controlled EPS production, at a range of air flow rates, was poor (<2 kg m(-3)). Biomass formation generally increased with increasing aeration rate. When culture pH was controlled at 4.5 +/- 0.2 EPS production was maximal at an air flow rate of 100 dm(3) min(-1) and fell as air flow rate decreased. Operation of the reactor at a high (100 dm(3) min(-1)) air flow rate for the early part of the process (up to 96 h), followed by a low air flow rate (20 dm(3) min(-1)), led to reduced biomass and oxalate formation, and a slight increase in EPS concentration relative to operation at a constant air flow rate of 100 dm(3) min(-1). EPS production in this pneumatically-agitated reactor was equal to the highest levels reported in small-scale stirred tank reactors.