Calculation of two-loop top-quark and Higgs-boson corrections in the electroweak standard model

A combination of algebraical and numerical techniques for calculating two-loop top-quark and Higgs-boson corrections to electroweak precision observables like Delta r or the rho-parameter is presented. The renormalization is performed within the on-shell scheme. The results of the calculations are valid for arbitrary values of m(t), M-H and of the gauge-boson masses. An example is treated where the full result is compared to the result obtained via an expansion up to next-to-leading order in m(t). As an application, results for the Higgs-mass dependent top-contributions to Delta r are given.