AbstractWe present the first results on galaxy metallicity evolution at z > 3 from two projects, LSD (Lyman-break galaxies Stellar populations and Dynamics) and AMAZE (Assessing the Mass Abundance redshift Evolution). These projects use deep near-infrared spectroscopic observations of a sample of ~40 LBGs to estimate the gas-phase metallicity from the emission lines. We derive the mass-metallicity relation at z > 3 and compare it with the same relation at lower redshift. Strong evolution from z = 0 and z = 2 to z = 3 is observed, and this finding puts strong constraints on the models of galaxy evolution. These preliminary results show that the effective oxygen yields do not increase with stellar mass, implying that the simple outflow model does not apply at z > 3.