  A U_L(3) \otimes U_R(3) low-energy effective lagrangian for the nonet of
pseudogoldstone bosons that appear in the large-Nc limit of QCD is presented
including terms up to four derivatives and explicit symmetry breaking terms up
to quadratic in the quark masses. The one-loop renormalization of the couplings
is worked out using the heat-kernel technique and dimensional renormalization.
The calculation is carried through for U_L(n_l) \otimes U_R(n_l), thus allowing
for a generic number n_l of light quark flavours. The crucial advantages that
the expansion in powers of 1/N_c bring about are discussed. Special emphasis is
put in pointing out what features are at variance with the SU_L \otimes SU_R
results when the singlet \eta' is included in the theory.
