  The recently-discovered Fundamental Metallicity Relation (FMR), which is the
tight dependence of metallicity on both mass and SFR, proves to be a very
useful tool to study the metallicity properties of various classes of galaxies.
We have used the FMR to study the galaxies hosting long-GRBs. While the GRB
hosts have lower metallicities than typical galaxies of the same mass, i.e.,
they are below the mass-metallicity relation, they are fully consistent with
the FMR. This shows that the difference with the mass-metallicity relation is
due to higher than average SFRs, and that GRBs with optical afterglows do not
preferentially select low-metallicity hosts among the star-forming galaxies.
