  We investigate the metal enrichment of elliptical galaxies in the framework
of hierarchical models of galaxy formation. The semi-analytical model we use in
this Letter, which has been used to study the metal enrichment of the
intracluster medium (ICM) by Nagashima et al., includes the effects of flows of
gas and metals both into and out of galaxies and the processes of metal
enrichment due to both type Ia and type II supernovae. We adopt a solar
neighbourhood IMF for star formation in discs, but consider models in which
starbursts have either a solar neighbourhood IMF or a top-heavy IMF. We find
that the alpha-element abundance in ellipticals is consistent with observed
values only if the top-heavy IMF is used. This result is consistent with our
previous study on the metal enrichment of the ICM. We also discuss the
abundance ratio of alpha elements to iron as a function of velocity dispersion
and metallicity. We find that models with a top-heavy IMF match the alpha/Fe
ratios observed in typical L_* ellipticals, but none of the models reproduce
the observed increase of alpha/Fe with velocity dispersion.
