  We analyze the acoustic attenuation rate in high-$T_c$ superconductors, and
find that this method offers an additional way to examine the anisotropy of the
superconducting order parameter in these materials. We argue that it should be
possible to distinguish the electronic contribution to the acoustic
attenuation, which has a strong temperature dependence near $T_c$, from the
lattice contribution, which does not show a strong temperature dependence near
$T_c$. We propose that this can be utilized to measure the anisotropy of the
order parameter by measuring the attenuation rate near $T_c$ in different
directions.
