Luminosity–metallicity relation for our sample of intermediate redshift star-forming galaxies (filled circles), compared with several other samples, shown as open symbols. The comparison samples are: (upper left) local star-forming galaxies from the NFGS; (upper right) intermediate redshift galaxies, 0.4 < z < 0.82, from Kobulnicky & Phillips (2003); (lower left) the galaxy sample of Lilly et al. (2003), with 0.47 < z < 0.92 and (lower right) luminous infrared galaxies with 0.4 < z < 1.16 from Liang et al. (2004). Oxygen abundances have been estimated assuming that all star-forming galaxies are on the upper branch of the relationship between R₂₃ parameter and 12 + log(O/H) (see text for more details).