A bioreactor system equipped with a hollow fiber cross-filtration module was used for continuous cultivation of Lactobacillus acidophilus at high cell concentrations. The growth rate did not correlate with the lactate concentration if the residual glucose concentration was kept nearly zero in the culture broth. To achieve this, an effective control method of medium feed rate was developed on the basis of the correlation between the specific glucose consumption rate (nu) and the specific cell growth rate (mu), i.e. nu = 2.90 mu + 0.39. Growth up to 50 g dry wt l(-1) was achieved without glucose accumulation under the total cell recycle. Via the partial cell recycle, continuous biomass production was achieved with a steady-state L. acidophilus concentration and dilution rate being 40 gl(-1) and 0.09 h(-1).