Acetone, butanol and ethanol were produced in a continuous two-stage fermentation integrated with pervaporation using freely suspended cells of C. acetobutylicum ATCC 824. PDMS composite pervaporation membranes were directly coupled to the second fermentor which lead to decreased solvent titers. Overall productivity was increased from 0.45gL<SUP>-1</SUP>h<SUP>-1</SUP> to 0.88gL<SUP>-1</SUP>h<SUP>-1</SUP> when increasing the carbohydrate concentration in the feed from 60 to 120gL<SUP>-1</SUP>. The highest overall productivity of 1.13gL<SUP>-1</SUP>h<SUP>-1</SUP> was achieved when increasing the carbohydrate concentration further to 150gL<SUP>-1</SUP> even though productivity decreased significantly in the first fermentor due to substrate inhibition. In this phase that lasted 200h, the average flux reached 0.621kgm<SUP>-2</SUP>h<SUP>-1</SUP> and the total solvent concentration in the permeate was 202gL<SUP>-1</SUP>. High solvent titers in the second fermentor were beneficial for the performance of the pervaporation unit leading to higher fluxes and total solvent concentrations in the permeate.