  We find the basic ingredients required to compute the Operator Product
Expansion of Wilson-'t Hooft operators in N=4 super-Yang-Mills theory with
gauge group G=PSU(3). These include the geometry of certain moduli spaces of
BPS configurations in the presence of 't Hooft operators and vector bundles
over them. The bundles arise in computing the OPE due to electric degrees of
freedom in dyonic operators. We verify our results by reproducing the OPE of 't
Hooft operators predicted by S-duality.
