  A Roy equation analysis of the available $\pi\pi$ phase shift data is
performed with the $I=0$ S- wave scattering length $a^0_0$ in the range
predicted by the one-loop standard chiral perturbation theory. A suitable
dispersive framework is developed to extract the chiral coupling constants
\lb{1}, \lb{2} and yields \lb{1}$=-1.70\pm0.15$ and \lb{2}$\approx 5.0$. We
remark on the implications of this determination to (combinations of) threshold
parameter predictions of the three lowest partial waves.
