H-DYONS AND S-DUALITY

We present a relatively simple argument showing that H-dyon states req uired by S-duality of the heterotic string on T-6 are present provided that the BPS dyons required by S-duality of N = 4 supersymmetric Yang -Mills theory are present. We also conjecture and provide evidence tha t H-dyons at singularities where the non-perturbative gauge symmetry i s completely broken behave like BPS dyons. (C) 1997 Elsevier Science B .V.