  Isospin diffusion in semi-peripheral collisions is probed as a function of
the dissipated energy by studying two systems $^{58}Ni$ + $^{58}Ni$ and
$^{58}Ni$ + $^{197}Au$, over the incident energy range 52-74\AM. A close
examination of the multiplicities of light products in the forward part of
phase space clearly shows an influence of the isospin of the target on the
neutron richness of these products. A progressive isospin diffusion is observed
when collisions become more central, in connection with the interaction time.
