An enhancement of the resistance due to the presence of only one or two iso
lated domain walls is clearly evidenced by transport measurements in 35 nm
epitaxial Co wires, 20 mu m long. The deduced relative change in the resist
ivity is at least 1 order of magnitude larger than the one predicted from a
model based on the mixing of spin channels occurring over the length scale
of the domain wall width [P.M. Levy and S. Zhang, Phys. Rev. Lett. 79, 511
0 (1997)]. This inconsistency can be resolved by taking the effect of spin
accumulation into account, which scales in the case of Co over the much lar
ger distance of the spin diffusion length.