  We have carried out a two loop computation of the low-energy effective action
for the four-dimensional N=2 supersymmetric Yang-Mills system coupled to
hypermultiplets, with the chiral superfields of the vector multiplet lying in
an abelian subalgebra. We have found a complete cancellation at the level of
the integrands of Feynman amplitudes, and therefore the two loop contribution
to the action, effective or Wilson, is identically zero.
