  We report the possible detection (99.3% of statistical significance) of
redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst
GRB970508 observed by BeppoSAX. Its energy is consistent with the redshift of
the putative host galaxy determined from optical spectroscopy. In contrast to
the fairly clean environment expected in the merging of two neutron stars, the
observed line properties would imply that the site of the burst is embedded in
a large mass of material ($>0.5 \Ms$), consistent with pre-explosion ejecta of
a very massive star. This material could be related with the outburst observed
in the afterglow 1 day after the GRB and with the spectral variations measured
during this phase. We did not find evidence of Fe line in two other GRB with
known redshift (GB971214 and GB980613), but we note that the upper limits are
of the same order of the intensity measured in GB97508 and that none of these
afterglows shows rebursting activity.
