  Studies of elemental abundances are a fundamental tool for unveiling the
nature of the high-redshift (proto-)galaxies associated to Damped Ly alpha
systems (DLAs). The present contribution analyses the impact of dust and
ionization effects on abundance measurements in DLAs. The behaviour of the
alpha/Fe abundance ratio corrected for such effects is used to derive
information on the chemical history and nature of DLA galaxies. The alpha/Fe
data indicate that DLAs at z~2.5 do not represent a homogeneous class of
objects. On average, DLAs show non-enhanced alpha/Fe ratios at low metallicity,
suggesting an origin in galaxies with low or intermittent star formation rates.
