  As a test of the gluon scattering amplitude/Wilson loop duality, we evaluate
the hexagonal light-like Wilson loop at two loops in N=4 super Yang-Mills
theory. We compare its finite part to the Bern-Dixon-Smirnov (BDS) conjecture
for the finite part of the six-gluon amplitude. We find that the two
expressions have the same behavior in the collinear limit, but they differ by a
non-trivial function of the three (dual) conformally invariant variables. This
implies that either the BDS conjecture or the gluon amplitude/Wilson loop
duality fails for the six-gluon amplitude, starting from two loops. Our results
are in qualitative agreement with the analysis of Alday and Maldacena of
scattering amplitudes with infinitely many external gluons.
