The efficiency of second-harmonic generation from chiral surfaces is d
ifferent for fundamental beams that are left- and right-hand circularl
y polarized or that have two appropriately chosen linear polarizations
. These effects can occur within the electric-dipole approximation. Ho
wever, for the case of thin films of chiral polymers, we provide evide
nce of magnetic-dipole contributions to this form of nonlinear optical
activity.