Two-loop effects of enhanced electroweak strength in the Higgs sector

The selfcoupling of the Higgs field grows with the mass of the Higgs particle and induces potentially large radiative corrections in the electroweak model. The technical aspects of performing multiloop calculations in the massive case are discussed briefly. I review the status of two-loop calculations of radiative corrections of enhanced electroweak strength which are relevant for the Higgs physics. I discuss the relevance of the existing results with respect to heavy Higgs searches at future colliders and their implications regarding the validity range of perturbation theory.