Cells of Clostridium acetobutylicum were immobilized by adsorption onto bonechar, and used in a packed bed or fluidized bed reactor for continuous production of ABE from whey permeate, At dilution rates in the range 0.35-1.10 h(-1), ABE productivity values of 3.0 to 4.0 g/l . h were observed, but lactose utilization values were poor. When operated in an integrated system with product removal by liquid-liquid extraction, there was a decrease in productivity but lactose utilization was increased markedly. Of the three extractants tested, oleyl alcohol was superior to both benzyl benzoate and dibutyl phthalate.