The yeast–mycelial dimorphic Aureobasidium pullulans var. pullulans was grown in chemostat culture under zinc-limitation at pH values in the range 2–7. Steady state was obtained and the growth yield with respect to zinc was independent of pH. The culture grew entirely as yeast, independently of the pH in the pH interval 3–7. The exopolysaccharide (EPS) production from the yeast cells was highest in the pH range 3–6 with a maximum at pH 4·0. Only little EPS was produced at pH 7·0 and no EPS was produced at pH 2·1. At pH 2·1 about 20% of the total biomass was in the filamentous growth form and some chlamydospores were present. A change in the carbon source from glucose to sucrose resulted in a more than doubling of the steady-state EPS concentration from 3·1 to 6·9 g l−1. A simple mass balance on carbon was constructed which could account for more than 95% of the carbon.