  The extension of Green's functions techniques to the complex energy plane
provides access to fully dressed quasi-particle properties from a microscopic
perspective. Using self-consistent ladder self-energies, we find both spectra
and lifetimes of such quasi-particles in nuclear matter. With a consistent
choice of the group velocity, the nucleon mean-free path can be computed. Our
results indicate that, for energies above 50 MeV at densities close to
saturation, a nucleon has a mean-free path of 4 to 5 femtometers.
