  We present early time, high resolution spectroscopy of three GRB afterglows:
GRB050730, GRB050922C and GRB060418. These data give us precious information on
the kinematics, ionization and metallicity of the interstellar matter of GRB
host galaxies up to a redshift z = 4, and of intervening absorbers along the
line of sight. The absorption spectra show that elements are present both with
high and low ionization states, and even forbidden, fine structure levels are
commonly observed. These features allow us to evaluate the physical parameters
of the absorbing gas. In details, the density of the gas regions lie in the
range n = 10 - 10^6 cm-3, and the temperatures are of the order of T = 10^3 -
10^4 K. The metallicity of the GRB host galaxies is computed using the hydrogen
absorption features. We find undersolar abundances for our GRBs, namely, Z =
0.001 - 0.01. However, depletion has not been considered. It can be taken into
account using as metallicity indicators Zn and Cr, which tend to remain in the
gas phase. We find metallicities higher than the previous values and in
agreement with other measurements for GRB host galaxies. Finally, the observed
[C/Fe] ratio for GRB050730 (z = 3.967) agrees with values expected for a galaxy
younger than a Gyr undergoing bursts of star-formation. In addition, the [C/Fe]
ratio evaluated component by component can give informations on the relative
distances of the components from the GRB explosion site, since Fe dust is more
efficiently destroyed than graphite.
