  Electron spin relaxation caused by the D'yakonov-Perel' mechanism is
investigated theoretically in asymmetrical A$_3$B$_5$ heterostructures. The
total spin relaxation anisotropy is demonstrated for a wide range of structure
parameters and temperatures. The spin relaxation rates dependences are derived
for GaAs-based heterojunction and triangular quantum well. The calculations
show a few orders of magnitude difference in spin relaxation times.
