  We study both the spin and electrical conductivities in models of relevance
to the high $T_c$ cuprates. These models describe metallic states with or
without spin-charge separation. We demonstrate that, given a linear in
temperature dependence of the electrical resistivity, the spin resistivity
should also be linear in temperature in the absence of spin-charge separation
and under conditions appropriate at least for the optimally doped cuprates, but
is in general {\it not} so in the presence of spin-charge separation. Based on
these results, we propose to use the temperature dependence of the electron
spin diffusion constant to diagnose spin-charge separation in the cuprates.
