  We present an extension of the string-inspired technique suitable to the
calculation of amplitudes and effective Lagrangians involving both vector and
axial vector gauge fields. The technique is easily adaptable to problems
involving constant external fields. We demonstrate the advantages of the
formalism by a calculation of the one-loop vector-axialvector amplitude in a
general constant electromagnetic field. The relevance of this calculation for
photon-neutrino processes is commented upon. We also clarify the properties of
the formalism with respect to the chiral symmetry, and its connection to second
order fermions.
