  We present the first results obtained from our pilot ultra-deep near-IR
survey with ISAAC/VLT, aimed at the detection of z>7 sources using lensing
clusters as natural Gravitational Telescopes. Evolutionary synthesis models of
PopIII and extremely metal-poor starbursts have been used to derive
observational properties expected for these high-z galaxies, such as expected
magnitudes and colors, line fluxes for the main emission lines, etc. These
models have allowed us to define fairly robust selection criteria to find z~
7-10 galaxies based on broad-band near-IR photometry in combination with the
traditional Lyman drop-out technique. The magnification in the core of lensing
clusters improves the search efficiency and subsequent spectroscopic follow up.
The method used to identify sources and the first results obtained are
presented, in particular the first spectroscopic confirmation of a z=10
candidate. The research efficiency will be significantly improved by the future
near-IR multi-object facilities such as EMIR/GTC and KMOS/VLT-2, and later by
the JWST.
