  Context: Stellar evolution theory suggests that the relationship between
number ratios of supernova (SN) types and metallicity holds important clues as
to the nature of the progenitor stars (mass, metallicity, rotation, binarity,
etc). Aims: We investigate the metallicity dependence of number ratios of
various SN types, using a large sample of SN along with information on their
radial position in, and magnitude of, their host galaxy. Methods: We derive
typical galaxian metallicities (using the well known metallicity-luminosity
relation) and local metallicities, i.e. at the position of the SN; in the
latter case, we use the empirical fact that the metallicity gradients in disk
galaxies are ~ constant when expressed in dex/R25. Results: We confirm a
dependence of the N(Ibc)/N(II) ratio on metallicity; recent single star models
with rotation and binary star models with no rotation appear to reproduce
equally well that metallicity dependence. The size of our sample does not allow
significant conclusions on the N(Ic)/N(Ib) ratio. Finally, we find an
unexpected metallicity dependence of the ratio of thermonuclear to core
collapse supernovae, which we interpret in terms of the star formation
properties of the host galaxies.
