The effects of osmotic pressure and dilution rate were investigated on the continuous production of glycerol in a multistage cascade bioreactor. The results showed that high osmotic pressure could improve fermentation performance significantly. At a dilution rate of 0.050 h(-1) and feeding 400 g l(-1) glucose solution, a glycerol yield of 25.0% based on glucose consumed and a maximum productivity of 19.4 g l(-1) per day were obtained, respectively, in a six-stage cascade bioreactor. When the dilution rate was increased from 0.023 to 0.085 h(-1) the glycerol yield, based on biomass, remained constant, but specific productivity increased by 94.7%. Productivity increased by only 46.6% due to low biomass concentration in the bioreactor at the higher dilution rates. (C) 2002 Elsevier Science Ltd. All rights reserved.