  Near-infrared spectra of 50 elliptical galaxies in the Pisces, A2199 and
A2634 clusters, and in the general field, have been obtained. The strength of
the CO (2.3 micron) absorption feature in these galaxies is used to explore the
presence of an intermediate-age population (e.g. Asymptotic Giant Branch stars)
in ellipticals in different environments. We find the strongest evidence for
such a population comes from ellipticals in groups of a few members, which we
interpret as the result of recent minor merging of these galaxies with later
type galaxies. Field galaxies from very isolated environments, on the other
hand, show no evidence for young or intermediate-age stars as revealed by H
beta and CO absorptions, and appear to form a very uniform, old population with
very little scatter in metallicity and star formation history.
