Abstract
ABSTRACT. A short review of the H, He, C, N and 0 enrichment of the in- terstellar medium is given. The following results are stressed: a) intermediate mass stars in the 1 to 8 M0 are the main producers of C, b) the predicted secondary N production by massive stars is roughly consistent with the observed He and N enrichment in extragalactic H II regions, c) for oxygen poor galaxies there is an excess of N relative to He which could imply an additional source of N or that infall has been important during the history of these systems, d) the contribution to the He and N enrichment of the ISM by planetary nebulae of Types II and III is negligible in comparison to that provided by planetary nebulae of Type I, e) the observed AY/Az value is in contradiction with simple models of galactic chemical evolution and/or conventional models of stellar evolution. Keq : ABUNDANCES - GALAXIES-EVOLUTION
