  Quark currents renormalization constants can in principle be safely computed
in lattice perturbation theory. In practice, traditional lattice perturbative
computations are quite cumbersome, so that so far only the first loop results
were available. By making use of Numerical Stochastic Perturbation Theory we
reached three (and with less statistical precision even four) loops, both in
quenched and in unquenched theory. Convergence properties of the series can be
assessed and omparison with non perturbative results (where available) can be
made: high loops computations of renormalization constants can be a valuable
tool for lattice QCD.
