Longitudinal gauge boson scattering can potentially be used to differentiate between different mechanisms of electroweak symmetry breaking; in particular between models with a heavy Higgs particle or with technicolor. The lowest order contribution to the scattering amplitude in an energy expansion (proportional to s) is fixed by the SU(2) symmetry of the theory. The O(s2) contributions, however, are quite sensitive to the symmetry breaking mechanism. Here we consider the one-loop radiative corrections due to heavy fermions on the energy expansion for longitudinal gauge boson scattering. We also present the effects of heavy fermions in the limit s ≫ MH 2, s ≫ Mt 2, and comment on their effect on unitarity bounds for the Higgs boson mass.