  We propose a general method to obtain accurate estimates for some of the
"low-energy constants" in the one-loop effective chiral Lagrangian by means of
simulating lattice QCD. In particular, the method is sensitive to those
constants whose values are required to test the hypothesis of a massless
up-quark. Initial tests performed in the quenched approximation confirm that
good statistical precision can be achieved. As a byproduct we obtain an
accurate estimate for the ratio of pseudoscalar decay constants, F_K/F_pi, in
the quenched approximation, which lies 10% below the experimental result. The
quantities that serve to extract the low-energy constants also allow a test of
the scaling behaviour of different discretizations of QCD and a search for the
effects of dynamical quarks.
