The non-factorizable two-loop corrections to
the formfactor both for a $U(1)\times U(1)$
and a $SU(2)\times U(1)$ gauge theory
with massive and massless gauge bosons respectively are evaluated at
arbitrary momentum transfer $q^2$.
The asymptotic behaviour for $q^2\to\infty$
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.