  For the first time, we compute non-perturbatively, i.e. without lattice
perturbation theory, the renormalization constants of two-fermion operators in
the quenched approximation at $\beta=6.0$, 6.2 and 6.4 using the Wilson and the
tree-level improved SW-Clover actions. We apply these renormalization constants
to fully non-perturbatively estimate quark masses in the $\bar{MS}$ scheme from
lattice simulations of both the hadron spectrum and the Axial Ward Identity in
the quenched approximation. Some very preliminary unquenched Wilson results
obtained from the gluon configurations generated by the T$\chi$L Collaboration
at $\beta=5.6$ and $N_{f}=2$ are also discussed.
