  We present an extension of the large $N_f$ formalism that allows to study
cases with multiple fermion representations. The pole structure in the beta
function is traced back to the intrinsic non-abelian nature of the gauge group,
independently on the fermion representation. This result validates the
conjectured existence of an interactive UV fixed point for non-abelian gauge
theories with large fermion multiplicity. Finally, we apply our results to
chiral gauge theories and to extended Grand Unified Theories.
