Exopolysaccharide (EPS) production and biosynthesis were studied in Ganoderma lucidum, a fungus used in traditional Chinese medicine, grown with lactose in a bioreactor. beta-Galactosidase activity, which implies the existence of a lactose permease system, was induced by lactose. Lactose feeding also increased alpha-phosphoglucomutase activity and EPS accumulation but decreased phosphoglucose isomerase activity and lactate concentration in the culture broth. A maximum cell density of 22 g l(-1) and EPS at 1.25 g l(-1) were obtained in fed-batch bioreactor culture.