We derive the spontaneous anisotropy of the resistivity of the ferromagnetic compound PrAh from magnetoresistance measurements on a single crystal of PrAlz. We ascribe this spontaneous anisotropy of the resistivity to scattering of the conduction electrons by the thermal quadrupole disorder and we account for our experimental results by using the theoretical model previously deve1oped by us. We find that quadrupole scattering gives a very important contribution to the total magnetic disorder (spin and quadrupole) resistivity but that only a small part of this quadrupole contribution is anisotropic
