Using the harmonic superspace background field formulation for general
D = 4, N = 2 super Yang-Mills theories, with matter hypermultiplets i
n arbitrary representations of the gauge group, we present the first r
igorous proof of the N=2 non-renormalization theorem; specifically: th
e absence of ultraviolet divergences beyond the one-loop level, Anothe
r simple consequence of the background field formulation is the absenc
e of the leading non-holomorphic correction to the low-energy effectiv
e action at two loops. (C) 1998 Published by Elsevier Science B.V. All
rights reserved.