A novel continuous annular packed-bed bioreactor for immobilized-cell fermentation was developed. In the operation of this bioreactor, the nongrowth medium was added to the immobilized-cell phase evenly and continuously through a stationary inlet. The nutrient medium, on the other hand, was fed to the bed through a rotating nozzle. Therefore, addition of the nutrient medium to every local point in the immobilized-cell phase was only intermittent whereas the whole process was continuous. For an alpha-amylase fermentation by kappa-carrageenan gel-immobilized Bacillus amyloliquefaciens cells, this bioreactor was found to be suitable for the control of cell growth and maintenance of cell productivity. Moreover, the volumetric productivity of a-amylase obtained in this bioreactor could be much higher than in a shake flask, if the reactor was properly operated.