  Numerical simulations predict that bars represent a very important agent for
triggering gas inflows, which in turn could lead to central star formation.
Bars thus are thought to contribute to the formation of the bulge.This changes
both, the gaseous-phase and stellar-phase metallicities in the centres of
galaxies. With the aim of quantifying the importance of this process we present
a comparative study of the gaseous-phase and stellar-phase metallicities in the
centres of members of a sample of barred and unbarred galaxies from SDSS. We do
not find a significant difference in the metallicity (neither gaseous nor
stellar) of barred and unbarred galaxies, but we find different trends in the
metallicities of early- and late- type galaxies, with larger differences in the
metallicity in the early-type subsample. Our results contradict some previous
research in this field, but we find a possible origin of the discrepancies
between previous works and our results.
