Aureobasidium pullulans forms an acidic extracellular polysaccharide when grown in liquid, shake or stationary cultures on a range of carbon sources and at different sugar concentrations. The polysaccharide contains glucose (90 %), malic acid (9 %), protein (3 %) and phosphate (0.5 %). The polysaccharide forms an insoluble complex with cetyl-trimethylammonium bromide from which it is recovered in more than 70% yield with the same composition as the original product. Periodate oxidation and Smith degradation indicate that the polysaccharide has 68 % (1 → 3) and 32 % (1 → 6) linkages. The infrared spectrum shows an absorption band at 890 cm −1 characteristic of β-configuration and a band at 1750 characteristic of the carbonyl (-CO-) group of saturated esters.