  We study the problem of calculating two-loop three-point diagrams with
irreducible numerators (i.e. numerators which cannot be expressed in terms of
the denominators). For the case of massless internal particles and arbitrary
(off-shell) external momenta, exact results are obtained in terms of
polylogarithms. We also consider the tensor decomposition of two-loop
three-point diagrams, and show how it is connected with irreducible numerators.
