  We examine the meson-baryon interaction in the strangeness S=-1 sector using
an effective chiral Lagrangian. Potentials are derived from this Lagrangian and
used in a coupled-channel calculation of the low energy observables. The
potentials are constructed such that in the Born approximation the s-wave
scattering amplitude is the same as that given by the effective chiral
Lagrangian, up to order $q^2$. Comparison is made with the available low energy
hadronic data of the coupled $K^-p, \Sigma \pi, \Lambda \pi$ system, which
includes the $\Lambda (1405)$ resonance, $K^-p$ elastic and inelastic
scattering, and the threshold branching ratios of the $K^-p$ decay. Good fits
to the experimental data and estimates of previously unknown Lagrangian
parameters are obtained.
