  We investigate the rectification of an ac bias in Luttinger liquids in the
presence of an asymmetric potential (the ratchet effect). We show that strong
repulsive electron interaction enhances the ratchet current in comparison with
Fermi liquid systems, and the I-V curve is strongly asymmetric in the
low-voltage regime even for a weak asymmetric potential. At higher voltages the
ratchet current exhibits an oscillatory voltage dependence.
