The effect of initial N and C source concentrations upon formation of scleroglucan from Sclerotium glucanicum was examined in batch cultures. Increasing the initial N source concentration led to an increased cell mass at the expense of scleroglucan. High initial C source concentrations (greater than or equal to 45 kg m(-3)) inhibited the microorganism significantly, leading to reduced product levels. Supplementation of batch cultures with additional sucrose after the initial growth phase could overcome these difficulties, improving polysaccharide broth concentration by up to 80% and improving yield of product on C source. The clear optimum time for supplementation was around 72 h, close to the point of N source exhaustion.