  The magnitude of $m_u,\,m_d$ and $m_s$ is discussed on the basis of Chiral
Perturbation Theory. In particular, the claim that $m_u=0$ leads to a coherent
picture for the low energy structure of QCD is examined in detail. It is
pointed out that this picture leads to violent flavour asymmetries in the
matrix elements of the scalar and pseudoscalar operators, which are in conflict
with the hypothesis that the light quark masses may be treated as
perturbations. [Talk delivered at the 2nd IFT Workshop, "Yukawa Couplings and
the Origins of Mass", Gainesville, Florida, Feb. 1994, to be published by
International Press.]
