  We present new high resolution spectroscopic observations of the intermediate
age (~2 Gyr) open cluster NGC 752. We investigate the Li vs. Teff distribution
and we obtain a new accurate determination of the cluster metallicity. We
compare the results for NGC 752 with other intermediate age and old clusters
spanning the age range from the Hyades (~0.6 Gyr) to NGC 188 (~6-8 Gyr). We
find that NGC 752 has a solar iron content ([Fe/H]=+0.01+/-0.04), at variance
with early reports of sub-solar metallicity. We find that NGC 752 is only
slightly more Li depleted than the younger Hyades and has a Li pattern almost
identical to that observed in the ~2 Gyr old IC 4651 and NGC 3680. As for the
latter clusters, we find that NGC 752 is characterized by a tight Li vs. Teff
distribution for solar-type stars, with no evidence for a Li spread as large as
the one observed in the solar age solar metallicity M 67. We discuss these
results in the framework of mixing mechanisms and Li depletion on the main
sequence (MS). We conclude that the development of a large scatter in Li
abundances in old open clusters might be an exception rather than the rule
(additional observations of old clusters are required), and that metallicity
variations of the order of ~0.2 dex do not affect Li depletion after the age of
the Hyades.
