Abstract: The present invention relates to a novel perfusion bioreactor allowing continuous medium feed and extraction of metabolites or other desired products from cells. The invention is useful for plant cell cultures but may also be used for mammalian cell cultures, insect cell cultures and bacterial cell cultures. The design of the reactor includes sedimentation columns mounted inside the bioreactor to separate single cells and cell aggregates from the culture medium at a very low shear stress. The operating conditions allow a stable cell/medium separation by maintaining the medium upward velocity equal to or slightly lower than the cell sedimentation velocity.