  Quantum loops in the Resonance Chiral Theory are needed to improve the
implementation of non-perturbative QCD. Furthermore, the one-loop computations
can predict chiral low-energy couplings at next-to-leading order, a very
appealing task. We present a first calculation of the vector form factor of the
pion at subleading order in the 1/N_C expansion. From the analysis of the
result at large energies we justify the requirement of considering
short-distance constraints from form factors with resonances in the final
state. The long-distance limit of our results allows to get a next-to-leading
order estimate of \ell_6.
