  The two-loop Sudakov form factor is computed in a U(1) model with a massive
gauge boson and a $U(1)\times U(1)$ model with mass gap. We analyze the result
in the context of hard and infrared evolution equations and establish a
matching procedure which relates the theories with and without mass gap setting
the stage for the complete calculation of the dominant two-loop corrections to
electroweak processes at high energy.
