The effect of culture pH upon exopolysaccharide (EPS), oxalic acid production, and biomass formation by Sclerotium glucanicum was examined in a stirred tank reactor. The optimum pH for EPS formation was 4.5; that for biomass was 3.5. Oxalate accumulation increased linearly above pH 3.5, probably as a result of stimulation of a synthetic enzyme (glyoxylate dehydrogenase) and reduced activity of a degradative enzyme. Up to 27% of the available carbon source could be diverted to oxalate formation at pH 5.5. By operating the process at pH 3.5 during the growth phase, and at pH 4.5 during the synthetic phase (afterNH(4)(+) exhaustion), EPS formation was significantly improved and oxalate formation was reduced to <10% of the concentration achieved at a fixed PH of 4.5.