  The $s-$wave meson-baryon scattering is analyzed for the strangeness S=0
sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral
Symmetry. Four channels have been considered: $\pi N$, $\eta N$, $K \Lambda$,
$K \Sigma$. The needed two particle irreducible matrix amplitude is taken from
lowest order Chiral Perturbation Theory in a relativistic formalism and low
energy constants are fitted to the elastic $\pi N $ phase-shifts and the $\pi^-
p \to \eta n$ and $\pi^- p \to K^0 \Lambda$ cross section data. The position of
the complex poles in the second Riemann sheet of the scattering amplitude
determine masses and widths of the $S_{11}-$ $N$(1535) and $-N$(1650)
resonances, in reasonable agreement with experiment. A good overall description
of data, from $\pi N$ threshold up to 2 GeV, is achieved keeping in mind that
the two pion production channel has not been included.
