  Observational evidence of iron absorption and emission lines in X-ray spectra
of Gamma-Ray Bursts is quite compelling. I will briefly review the results,
summarize different models and describe the connection with massive progenitors
in star-forming regions implied by these results. This link is also supported
by measurements of the X-ray absorbing gas in several GRB's, with column
density consistent with that of Giant Molecular Clouds harbouring
star-formation in our Galaxy, as well as by evidences gathered in other
wavelengths. However, the volume density inferred by the fireball-jet model is
much lower than typical of a GMC, and I will confront this with the alternative
explanation of fireball expansion in a high dense medium, outlining the
problems that both models have at present. Finally I will briefly summarize
some results on dark GRB's, and describe the prospects of high resolution X-ray
spectroscopy in getting closer to the central environment of GRB, and far in
the Early Universe by using GRB as beacons to probe star and galaxy formation.
