  We discuss the existence of a mass-metallicity relation among galactic halo
globular clusters. The lack of any luminosity-metallicity correlation in
globular cluster systems has been used as an argument against self-enrichment
models of cluster formation. We show that such a relation is statistically
present among the galactic Old Halo globulars. This observational correlation
implies that the least massive old clusters are the most metal-rich. This is in
contradiction with the idea that, if globular clusters were self-enriched
systems, the most metal-rich clusters would also be the most massive ones. We
further show that this anti-correlation is as predicted by self-enrichment
models.
