  For a large class of two-loop selfenergy- and vertex-type diagrams with only
one non-zero mass ($M$) and the vertices also with only one non-zero external
momentum squared ($q^2$) the first few expansion coefficients are calculated by
the large mass expansion. This allows to `guess' the general structure of these
coefficients and to verify them in terms of certain classes of `basis
elements', which are essentially harmonic sums. Since for this case with only
one non-zero mass the large mass expansion and the Taylor series in terms of
$q^2$ are identical, this approach yields analytic expressions of the Taylor
coefficients, from which the diagram can be easily evaluated numerically in a
large domain of the complex $q^2-$plane by well known methods. It is also
possible to sum the Taylor series and present the results in terms of
polylogarithms.
