Résumé
A chemical study of normal Galactic C(N) carbon stars is presented. Abundances of Li, CNO isotopes and s-elements are derived. The derived abundances of s-elements nicely agree with theoretical s-process nucleosynthesis predictions during the AGB phase. However, the figures obtained for Li and the C-12/C-13 ratios might imply the existence of a non-standard mixing process during the AGB phase operating preferentially in low mass stars. The intrinsic or extrinsic nature of C(N) stars is also discussed.