Clostridium beijerinckii DSM 6423 was studied using different continuous production methods to give maximum and stable production of isopropanol and n-butanol. In a single-stage continuous culture, when wood pulp was added as a cell holding material, we could increase the solvent productivity from 0.47 to 5.52 g L-1 h(-1) with the yield of 54% from glucose. The overall solvent concentration of 7.51 g L-1 (39.4% isopropanol and 60.6% n-butanol) with the maximum solvent productivity of 0.84 g L-1 h(-1) was obtained with two-stage continuous culture. We were able to run the process for more than 48 overall retention times without losing the ability to produce solvents.