  We develop a coupled channel unitary approach describing the behavior at
higher energies of systems whose low-energy dynamics is given by effective
O(p^2) and O(p^4) chiral Lagrangians. Our free parameters are those of the
O(p^4) Lagrangian. When applied to the meson-meson interaction, it yields a
remarkable agreement with data up to sqrt{s}=1.2 GeV, dynamically generating
the sigma, f_0, a_0,rho and K^* resonances. Further applications are also
proposed.
