The effects of organic acid supplementation on both yields and molecular weight distributions of exopolysaccharide (EPS) of Antrodia camphorata were investigated in shaker flasks and air-lift bioreactors. In the shaker flask study, five out of six organic acid-supplemented cultures showed negative effects on cell growth, the exception being pyruvic acid-supplemented culture; lower number average molecular weights (Mn) of EPS were obtained in all the supplemented cultures. EPS production was enhanced by 31% due to the addition of succinic acid. Optimum product yield was obtained between 2.0 and 3.0 g dm(-3) succinic acid; however, the specific production of EPS increased monotonically as succinic acid concentration was increased from 0 to 5 g dm(-3). Enhancement of EPS yield by 28% and a higher Mn of EPS (around 310kDa) due to the addition of succinic acid were also demonstrated in an air-lift bioreactor. In addition, a novel fermentation process resistant to EPS degradation is proposed, based on the inhibition of beta-glucanase activity by the supplementation with succinic acid. (C) 2004 Society of Chemical Industry.