  The scalar two-loop master diagram is revisited in the massive cases needed
for the computation of boson and fermion propagators in QED and QCD. By means
of the causal method it is possible in a straightforward manner to express the
propagators as double integrals. In the case of vacuum polarization both
integrations can be carried out in terms of polylogarithms, whereas the last
integral in the fermion propagator cannot be expressed by known special
functions. The advantage of the method in comparison with Feynman integral
calculations is indicated.
