We 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 metallicity from
emission lines. We derive the mass-metallicity relation at z>3 and
compare it with the same relation at lower redshift. A strong
evolution from z=2 to z=3, and can be use to put strong constraints on
the models of galaxy evolution involving stellar winds, AGN feedback
and galaxy merging.