CNO evolution: Milky Way, dwarf galaxies and DLAS

We compute the evolution of the C, N, O and Fe abundances as a function of time and galactocentric distance in the Milky Way ( MW) for different sets of stellar yields. We then apply the 'best' nucleosynthesis prescriptions found for the MW to other galaxies. Our main conclusions are: a) once the available observational data are properly interpreted, there is no compelling evidence for requiring an important production of primary N in massive stars; b) both C and N we see today in the ISM come mainly from low- and intermediate-mass stars.