Probing the Standard Model through radiative corrections

I report about the computation of quantum corrections to Standard Model observables, in particular the QCD corrections to Flavor Changing Neutral Currents decays of the b-quark, which are found to enhance very significantly the lowest order branching ratios of rare processes, like the b->s gamma decay; and the weak two-loop radiative corrections to LEP observables, particularly the rho parameter and the Z-> b bbar, in the limit of dominance of heavy top and Higgs exchanges. The inclusive B.R of the b->s gamma decay has been later measured by the CLEO collaboration, and the QCD corrections have been found crucial for the agreement with the theoretical predictions. The two-loop heavy top effects have been found instead to be less dramatic, and contributed to the confidence that quantum corrections to LEP observables are well under control.