We construct a classical field theory action which upon quantization via the
functional integral approach, gives rise to a consistent Dirac-string
independent quantum field theory. The approach entails a systematic derivation
of the correlators of all gauge invariant observables, and also of charged
dyonic fields. Manifest SO(2)-duality invariance and Lorentz invariance are
ensured by the PST-approach.Comment: 9 pages, LaTeX, talk given at the conference "Quantum aspects of
gauge theories, supersymmetry and unification", Paris, September 199
