  We derive the two-loop corrections to Bhabha scattering from heavy fermions
using dispersion relations. The double-box contributions are expressed by three
kernel functions. Convoluting the perturbative kernels with fermionic threshold
functions or with hadronic data allows to determine numerical results for small
electron mass m_e, combined with arbitrary values of the fermion mass m_f in
the loop, $m_e^2<<s,t,m_f^2$, or with hadronic insertions. We present numerical
results for m_f = m_{\mu}, m_{\tau}, m_{top} at typical small- and large-angle
kinematics ranging from 1 GeV to 500 GeV.
