  We address the question if one can empirically distinguish between the two
proposed solutions to the ``$U_A (1)$ problem'': the 't Hooft, and the
Veneziano-Witten $U_{A}(1)$ symmetry breaking effective interactions. Two
hadronic observables are offered as discriminants: (1) The scalar ($0^{+}$)
meson spectrum; (2) Weinberg's second spectral sum rule. Their present
experimental status is discussed.
