  The two-loop formfactor both for a U(1)xU(1) and a SU(2)xU(1) gauge theory
with massive and massless gauge bosons respectively is evaluated at arbitrary
momentum transfer q^2. The asymptotic behaviour for q^2->\infinity is compared
to a recent calculation of Sudakov logarithms. The result is an important
ingredient for the calculation of radiative corrections to Z-boson production
at hadron and lepton colliders.
