  The high-energy quark-quark scattering amplitude is calculated first in the
case of scalar QCD, using Fradkin's approach to derive the scalar quark
propagator in an external gluon field and computing it in the eikonal
approximation. The results are then extended to the case of ``real'' (i.e.,
fermion) QCD. The high-energy quark-quark scattering amplitude turns out to be
described by the expectation value of two lightlike Wilson lines, running along
the classical trajectories of the two colliding particles. Interesting analytic
properties of the high-energy quark-quark scattering amplitude can be derived,
going from Minkowskian to Euclidean theory: they could open the possibility of
evaluating the high-energy scattering amplitude directly on the lattice.
